diff --git a/vlib/crypto/rand/rand_test.v b/vlib/crypto/rand/rand_test.v
deleted file mode 100644
index 42021d243f..0000000000
--- a/vlib/crypto/rand/rand_test.v
+++ /dev/null
@@ -1,44 +0,0 @@
-// Copyright (c) 2019-2020 Alexander Medvednikov. All rights reserved.
-// Use of this source code is governed by an MIT license
-// that can be found in the LICENSE file.
-import crypto.rand
-
-fn get_random_bytes(no_bytes int) []byte {
-	r := rand.read(no_bytes) or {
-		assert false
-		return []
-	}
-	assert r.len == no_bytes
-	return r
-}
-
-fn test_crypto_rand_read() {
-	no_bytes := 100
-	r1 := get_random_bytes(no_bytes)
-	r2 := get_random_bytes(no_bytes)
-	mut equals := 0
-	for i in 0 .. r1.len {
-		if r1[i] == r2[i] {
-			equals++
-		}
-	}
-	assert (100.0 * f32(equals) / f32(no_bytes)) < 20.0
-}
-
-fn test_crypto_rand_int_u64() {
-	max := u64(160)
-	mut unique := []u64{}
-	for _ in 0 .. 80 {
-		r := rand.int_u64(max) or {
-			assert false
-			return
-		}
-		if r >= max {
-			assert false
-		}
-		if r !in unique {
-			unique << r
-		}
-	}
-	assert unique.len >= 10
-}
diff --git a/vlib/rand/mt19937.v b/vlib/rand/mt19937.v
index 3fa7bf239b..26afac7109 100644
--- a/vlib/rand/mt19937.v
+++ b/vlib/rand/mt19937.v
@@ -234,7 +234,7 @@ pub fn (mut rng MT19937RNG) intn(max int) int {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return int(rng.u32n(max))
+	return int(rng.u32n(u32(max)))
 }
 
 // rng.i64n(max) - return a 64bit positive i64 in [0, max)
@@ -244,7 +244,7 @@ pub fn (mut rng MT19937RNG) i64n(max i64) i64 {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return i64(rng.u64n(max))
+	return i64(rng.u64n(u64(max)))
 }
 
 // rng.int_in_range(min, max) - return a 32bit positive int in [0, max)
diff --git a/vlib/rand/mt19937_test.v b/vlib/rand/mt19937_test.v
index a392073b9c..068af67a52 100644
--- a/vlib/rand/mt19937_test.v
+++ b/vlib/rand/mt19937_test.v
@@ -14,7 +14,7 @@ const (
 )
 
 fn mt19937_basic_test() {
-	rng := rand.MT19937RNG{}
+	mut rng := rand.MT19937RNG{}
 	rng.seed([u32(0xdeadbeef)])
 	target := [956529277, 3842322136, 3319553134, 1843186657, 2704993644, 595827513, 938518626,
 		1676224337, 3221315650, 1819026461]
@@ -73,7 +73,7 @@ fn test_mt19937_variability() {
 	}
 }
 
-fn check_uniformity_u64(rng rand.MT19937RNG, range u64) {
+fn check_uniformity_u64(mut rng rand.MT19937RNG, range u64) {
 	range_f64 := f64(range)
 	expected_mean := range_f64 / 2.0
 	mut variance := 0.0
@@ -94,12 +94,12 @@ fn test_mt19937_uniformity_u64() {
 		mut rng := rand.MT19937RNG{}
 		rng.seed(seed)
 		for range in ranges {
-			check_uniformity_u64(rng, range)
+			check_uniformity_u64(mut rng, u64(range))
 		}
 	}
 }
 
-fn check_uniformity_f64(rng rand.MT19937RNG) {
+fn check_uniformity_f64(mut rng rand.MT19937RNG) {
 	expected_mean := 0.5
 	mut variance := 0.0
 	for _ in 0 .. sample_size {
@@ -118,7 +118,7 @@ fn test_mt19937_uniformity_f64() {
 	for seed in seeds {
 		mut rng := rand.MT19937RNG{}
 		rng.seed(seed)
-		check_uniformity_f64(rng)
+		check_uniformity_f64(mut rng)
 	}
 }
 
@@ -128,7 +128,7 @@ fn test_mt19937_u32n() {
 		mut rng := rand.MT19937RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
-			value := rng.u32n(max)
+			value := rng.u32n(u32(max))
 			assert value >= 0
 			assert value < max
 		}
@@ -155,7 +155,7 @@ fn test_mt19937_u32_in_range() {
 		mut rng := rand.MT19937RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
-			value := rng.u32_in_range(min, max)
+			value := rng.u32_in_range(u32(min), u32(max))
 			assert value >= min
 			assert value < max
 		}
@@ -210,7 +210,7 @@ fn test_mt19937_int63() {
 fn test_mt19937_intn() {
 	max := 2525642
 	for seed in seeds {
-		rng := rand.MT19937RNG{}
+		mut rng := rand.MT19937RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.intn(max)
@@ -223,7 +223,7 @@ fn test_mt19937_intn() {
 fn test_mt19937_i64n() {
 	max := i64(3246727724653636)
 	for seed in seeds {
-		rng := rand.MT19937RNG{}
+		mut rng := rand.MT19937RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.i64n(max)
@@ -237,7 +237,7 @@ fn test_mt19937_int_in_range() {
 	min := -4252
 	max := 1034
 	for seed in seeds {
-		rng := rand.MT19937RNG{}
+		mut rng := rand.MT19937RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.int_in_range(min, max)
@@ -251,7 +251,7 @@ fn test_mt19937_i64_in_range() {
 	min := i64(-24095)
 	max := i64(324058)
 	for seed in seeds {
-		rng := rand.MT19937RNG{}
+		mut rng := rand.MT19937RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.i64_in_range(min, max)
diff --git a/vlib/rand/musl_rng.v b/vlib/rand/musl_rng.v
index 0cb05ec88a..8adb0211b8 100644
--- a/vlib/rand/musl_rng.v
+++ b/vlib/rand/musl_rng.v
@@ -106,7 +106,7 @@ pub fn (mut rng MuslRNG) u32_in_range(min, max u64) u64 {
 		eprintln('max must be greater than min')
 		exit(1)
 	}
-	return min + rng.u32n(max - min)
+	return min + rng.u32n(u32(max - min))
 }
 
 // rn.u64_in_range(min, max) - return a pseudorandom 64 bit unsigned u64 in [min, max)
@@ -150,7 +150,7 @@ pub fn (mut rng MuslRNG) intn(max int) int {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return int(rng.u32n(max))
+	return int(rng.u32n(u32(max)))
 }
 
 // rng.i64n(max) - return a 64bit positive i64 in [0, max)
@@ -160,7 +160,7 @@ pub fn (mut rng MuslRNG) i64n(max i64) i64 {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return i64(rng.u64n(max))
+	return i64(rng.u64n(u64(max)))
 }
 
 // rng.int_in_range(min, max) - return a 32bit positive int in [0, max)
diff --git a/vlib/rand/musl_rng_test.v b/vlib/rand/musl_rng_test.v
index 45c8d86a91..c59514a742 100644
--- a/vlib/rand/musl_rng_test.v
+++ b/vlib/rand/musl_rng_test.v
@@ -63,7 +63,7 @@ fn test_musl_variability() {
 	}
 }
 
-fn check_uniformity_u64(rng rand.MuslRNG, range u64) {
+fn check_uniformity_u64(mut rng rand.MuslRNG, range u64) {
 	range_f64 := f64(range)
 	expected_mean := range_f64 / 2.0
 	mut variance := 0.0
@@ -84,12 +84,12 @@ fn test_musl_uniformity_u64() {
 		mut rng := rand.MuslRNG{}
 		rng.seed(seed)
 		for range in ranges {
-			check_uniformity_u64(rng, range)
+			check_uniformity_u64(mut rng, u64(range))
 		}
 	}
 }
 
-fn check_uniformity_f64(rng rand.MuslRNG) {
+fn check_uniformity_f64(mut rng rand.MuslRNG) {
 	expected_mean := 0.5
 	mut variance := 0.0
 	for _ in 0 .. sample_size {
@@ -108,7 +108,7 @@ fn test_musl_uniformity_f64() {
 	for seed in seeds {
 		mut rng := rand.MuslRNG{}
 		rng.seed(seed)
-		check_uniformity_f64(rng)
+		check_uniformity_f64(mut rng)
 	}
 }
 
@@ -118,7 +118,7 @@ fn test_musl_u32n() {
 		mut rng := rand.MuslRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
-			value := rng.u32n(max)
+			value := rng.u32n(u32(max))
 			assert value >= 0
 			assert value < max
 		}
@@ -145,7 +145,7 @@ fn test_musl_u32_in_range() {
 		mut rng := rand.MuslRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
-			value := rng.u32_in_range(min, max)
+			value := rng.u32_in_range(u64(min), u64(max))
 			assert value >= min
 			assert value < max
 		}
@@ -200,7 +200,7 @@ fn test_musl_int63() {
 fn test_musl_intn() {
 	max := 2525642
 	for seed in seeds {
-		rng := rand.MuslRNG{}
+		mut rng := rand.MuslRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.intn(max)
@@ -213,7 +213,7 @@ fn test_musl_intn() {
 fn test_musl_i64n() {
 	max := i64(3246727724653636)
 	for seed in seeds {
-		rng := rand.MuslRNG{}
+		mut rng := rand.MuslRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.i64n(max)
@@ -227,7 +227,7 @@ fn test_musl_int_in_range() {
 	min := -4252
 	max := 1034
 	for seed in seeds {
-		rng := rand.MuslRNG{}
+		mut rng := rand.MuslRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.int_in_range(min, max)
@@ -241,7 +241,7 @@ fn test_musl_i64_in_range() {
 	min := i64(-24095)
 	max := i64(324058)
 	for seed in seeds {
-		rng := rand.MuslRNG{}
+		mut rng := rand.MuslRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.i64_in_range(min, max)
diff --git a/vlib/rand/pcg32.v b/vlib/rand/pcg32.v
index 769ddb56fa..96fa6f88c1 100644
--- a/vlib/rand/pcg32.v
+++ b/vlib/rand/pcg32.v
@@ -14,7 +14,7 @@ mut:
 
 // TODO: Remove in Phase 2 of reorganizing Random
 pub fn new_pcg32(init_state, init_seq u64) PCG32RNG {
-	rng := PCG32RNG{}
+	mut rng := PCG32RNG{}
 	rng.seed([u32(init_state), u32(init_state >> 32), u32(init_seq), u32(init_seq >> 32)])
 	return rng
 }
@@ -104,7 +104,7 @@ pub fn (mut rng PCG32RNG) u32_in_range(min, max u64) u64 {
 		eprintln('max must be greater than min')
 		exit(1)
 	}
-	return min + rng.u32n(max - min)
+	return min + rng.u32n(u32(max - min))
 }
 
 // rn.u64_in_range(min, max) - return a pseudorandom 64 bit unsigned u64 in [min, max)
@@ -148,7 +148,7 @@ pub fn (mut rng PCG32RNG) intn(max int) int {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return int(rng.u32n(max))
+	return int(rng.u32n(u32(max)))
 }
 
 // rng.i64n(max) - return a 64bit positive i64 in [0, max)
@@ -158,7 +158,7 @@ pub fn (mut rng PCG32RNG) i64n(max i64) i64 {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return i64(rng.u64n(max))
+	return i64(rng.u64n(u64(max)))
 }
 
 // rng.int_in_range(min, max) - return a 32bit positive int in [0, max)
diff --git a/vlib/rand/pcg32_test.v b/vlib/rand/pcg32_test.v
index 0476176069..642f6c419d 100644
--- a/vlib/rand/pcg32_test.v
+++ b/vlib/rand/pcg32_test.v
@@ -61,7 +61,7 @@ fn test_pcg32_variability() {
 	}
 }
 
-fn check_uniformity_u64(rng rand.PCG32RNG, range u64) {
+fn check_uniformity_u64(mut rng rand.PCG32RNG, range u64) {
 	range_f64 := f64(range)
 	expected_mean := range_f64 / 2.0
 	mut variance := 0.0
@@ -82,12 +82,12 @@ fn test_pcg32_uniformity_u64() {
 		mut rng := rand.PCG32RNG{}
 		rng.seed(seed)
 		for range in ranges {
-			check_uniformity_u64(rng, range)
+			check_uniformity_u64(mut rng, u64(range))
 		}
 	}
 }
 
-fn check_uniformity_f64(rng rand.PCG32RNG) {
+fn check_uniformity_f64(mut rng rand.PCG32RNG) {
 	expected_mean := 0.5
 	mut variance := 0.0
 	for _ in 0 .. sample_size {
@@ -106,7 +106,7 @@ fn test_pcg32_uniformity_f64() {
 	for seed in seeds {
 		mut rng := rand.PCG32RNG{}
 		rng.seed(seed)
-		check_uniformity_f64(rng)
+		check_uniformity_f64(mut rng)
 	}
 }
 
@@ -116,7 +116,7 @@ fn test_pcg32_u32n() {
 		mut rng := rand.PCG32RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
-			value := rng.u32n(max)
+			value := rng.u32n(u32(max))
 			assert value >= 0
 			assert value < max
 		}
@@ -143,7 +143,7 @@ fn test_pcg32_u32_in_range() {
 		mut rng := rand.PCG32RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
-			value := rng.u32_in_range(min, max)
+			value := rng.u32_in_range(u64(min), u64(max))
 			assert value >= min
 			assert value < max
 		}
@@ -198,7 +198,7 @@ fn test_pcg32_int63() {
 fn test_pcg32_intn() {
 	max := 2525642
 	for seed in seeds {
-		rng := rand.PCG32RNG{}
+		mut rng := rand.PCG32RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.intn(max)
@@ -211,7 +211,7 @@ fn test_pcg32_intn() {
 fn test_pcg32_i64n() {
 	max := i64(3246727724653636)
 	for seed in seeds {
-		rng := rand.PCG32RNG{}
+		mut rng := rand.PCG32RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.i64n(max)
@@ -225,7 +225,7 @@ fn test_pcg32_int_in_range() {
 	min := -4252
 	max := 1034
 	for seed in seeds {
-		rng := rand.PCG32RNG{}
+		mut rng := rand.PCG32RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.int_in_range(min, max)
@@ -239,7 +239,7 @@ fn test_pcg32_i64_in_range() {
 	min := i64(-24095)
 	max := i64(324058)
 	for seed in seeds {
-		rng := rand.PCG32RNG{}
+		mut rng := rand.PCG32RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.i64_in_range(min, max)
diff --git a/vlib/rand/rand.v b/vlib/rand/rand.v
index cb39509267..d734bae99f 100644
--- a/vlib/rand/rand.v
+++ b/vlib/rand/rand.v
@@ -27,10 +27,6 @@ pub fn rand_r(seed &int) int {
 	return ns & 0x7fffffff
 }
 
-const (
-	default_rng = new_default({})
-)
-
 pub struct PRNGConfigStruct {
 	seed []u32 = time_seed_array(2)
 }
@@ -41,109 +37,6 @@ pub fn new_default(config PRNGConfigStruct) &WyRandRNG {
 	return rng
 }
 
-
-// u32() - returns a uniformly distributed pseudorandom 32-bit unsigned u32
-pub fn u32() u32 {
-	return default_rng.u32()
-}
-
-// u64() - returns a uniformly distributed pseudorandom 64-bit unsigned u64
-pub fn u64() u64 {
-	return default_rng.u64()
-}
-
-// u32n(max) - returns a uniformly distributed pseudorandom 32-bit unsigned u32 in [0, max)
-pub fn u32n(max u32) u32 {
-	return default_rng.u32n(max)
-}
-
-// u64n(max) - returns a uniformly distributed pseudorandom 64-bit unsigned u64 in [0, max)
-pub fn u64n(max u64) u64 {
-	return default_rng.u64n(max)
-}
-
-// u32n() - returns a uniformly distributed pseudorandom 32-bit unsigned u32 in [min, max)
-pub fn u32_in_range(min, max u32) u32 {
-	return default_rng.u32_in_range(min, max)
-}
-
-// u64_in_range(min, max) - returns a uniformly distributed pseudorandom 64-bit unsigned u64 in [min, max)
-pub fn u64_in_range(min, max u64) u64 {
-	return default_rng.u64_in_range(min, max)
-}
-
-// int() - returns a uniformly distributed pseudorandom 32-bit signed (possibly negative) int
-pub fn int() int {
-	return default_rng.int()
-}
-
-// intn(max) - returns a uniformly distributed pseudorandom 32-bit signed positive int in [0, max)
-pub fn intn(max int) int {
-	return default_rng.intn(max)
-}
-
-// int_in_range(min, max) - returns a uniformly distributed pseudorandom
-// 32-bit signed int in [min, max)
-pub fn int_in_range(min, max int) int {
-	return default_rng.int_in_range(min, max)
-}
-
-// int31() - returns a uniformly distributed pseudorandom 31-bit signed positive int
-pub fn int31() int {
-	return default_rng.int31()
-}
-
-// i64() - returns a uniformly distributed pseudorandom 64-bit signed (possibly negative) i64
-pub fn i64() i64 {
-	return default_rng.i64()
-}
-
-// i64n(max) - returns a uniformly distributed pseudorandom 64-bit signed positive i64 in [0, max)
-pub fn i64n(max i64) i64 {
-	return default_rng.i64n(max)
-}
-
-// i64_in_range(min, max) - returns a uniformly distributed pseudorandom
-// 64-bit signed int in [min, max)
-pub fn i64_in_range(min, max i64) i64 {
-	return default_rng.i64_in_range(min, max)
-}
-
-// int63() - returns a uniformly distributed pseudorandom 63-bit signed positive int
-pub fn int63() i64 {
-	return default_rng.int63()
-}
-
-// f32() - returns a uniformly distributed 32-bit floating point in [0, 1)
-pub fn f32() f32 {
-	return default_rng.f32()
-}
-
-// f64() - returns a uniformly distributed 64-bit floating point in [0, 1)
-pub fn f64() f64 {
-	return default_rng.f64()
-}
-
-// f32n() - returns a uniformly distributed 32-bit floating point in [0, max)
-pub fn f32n(max f32) f32 {
-	return default_rng.f32n(max)
-}
-
-// f64n() - returns a uniformly distributed 64-bit floating point in [0, max)
-pub fn f64n(max f64) f64 {
-	return default_rng.f64n(max)
-}
-
-// f32_in_range(min, max) - returns a uniformly distributed 32-bit floating point in [min, max)
-pub fn f32_in_range(min, max f32) f32 {
-	return default_rng.f32_in_range(min, max)
-}
-
-// f64_in_range(min, max) - returns a uniformly distributed 64-bit floating point in [min, max)
-pub fn f64_in_range(min, max f64) f64 {
-	return default_rng.f64_in_range(min, max)
-}
-
 // rand_f32 return a random f32 between 0 and max
 [deprecated]
 pub fn rand_f32(max f32) f32 {
diff --git a/vlib/rand/random_numbers_test.v b/vlib/rand/random_numbers_test.v
index 605b8a0dea..bcebc2b237 100644
--- a/vlib/rand/random_numbers_test.v
+++ b/vlib/rand/random_numbers_test.v
@@ -54,210 +54,3 @@ fn assert_randoms_equal(r1, r2 []int) {
 	}
 }
 
-fn test_rand_f32_old() {
-	for seed in seeds {
-		rand.seed(seed)
-		for _ in 0 .. rnd_count {
-			res := rand.rand_f32(100.0)
-			assert res >= 0.0
-			assert res < 100.0
-		}
-	}
-}
-
-fn test_rand_f32_in_range_old() {
-	for seed in seeds {
-		rand.seed(seed)
-		for _ in 0 .. rnd_count {
-			res := rand.rand_f32_in_range(1.0, 2048.0)
-			assert res >= 1.0
-			assert res < 2048.0
-		}
-	}
-}
-
-fn test_rand_f64_old() {
-	for seed in seeds {
-		rand.seed(seed)
-		for _ in 0 .. rnd_count {
-			res := rand.rand_f64(100.0)
-			assert res >= 0.0
-			assert res < 100.0
-		}
-	}
-}
-
-fn test_rand_f64_in_range_old() {
-	for seed in seeds {
-		rand.seed(seed)
-		for _ in 0 .. rnd_count {
-			res := rand.rand_f64_in_range(1.0, 2048.0)
-			assert res >= 1.0
-			assert res < 2048.0
-		}
-	}
-}
-
-fn test_rand_uniform_f32() {
-	for seed in seeds {
-		rand.seed(seed)
-		for _ in 0 .. rnd_count {
-			res := rand.rand_uniform_f32()
-			assert res >= 0.0
-			assert res < 1.0
-		}
-	}
-}
-
-fn test_rand_uniform_f64() {
-	for seed in seeds {
-		rand.seed(seed)
-		for _ in 0 .. rnd_count {
-			res := rand.rand_uniform_f64()
-			assert res >= 0.0
-			assert res < 1.0
-		}
-	}
-}
-
-fn test_rand_u32n() {
-	max := u32(4287502)
-	for _ in 0 .. rnd_count {
-		assert rand.u32n(max) < max
-	}
-}
-
-fn test_rand_u64n() {
-	max := u64(23442353534587502)
-	for _ in 0 .. rnd_count {
-		assert rand.u64n(max) < max
-	}
-}
-
-fn test_rand_u32_in_range() {
-	min := u32(5256)
-	max := u32(4287502)
-	for _ in 0 .. rnd_count {
-		value := rand.u32_in_range(min, max)
-		assert value >= min
-		assert value < max
-	}
-}
-
-fn test_rand_u64_in_range() {
-	min := u64(4265266246)
-	max := u64(23442353534587502)
-	for _ in 0 .. rnd_count {
-		value := rand.u64_in_range(min, max)
-		assert value >= min
-		assert value < max
-	}
-}
-
-fn test_rand_intn() {
-	max := 720948723
-	for _ in 0 .. rnd_count {
-		value := rand.intn(max)
-		assert value >= 0
-		assert value < max
-	}
-}
-
-fn test_rand_i64n() {
-	max := i64(209487239094)
-	for _ in 0 .. rnd_count {
-		value := rand.i64n(max)
-		assert value >= 0
-		assert value < max
-	}
-}
-
-fn test_rand_int_in_range() {
-	min := -34058
-	max := -10542
-	for _ in 0 .. rnd_count {
-		value := rand.int_in_range(min, max)
-		assert value >= min
-		assert value < max
-	}
-}
-
-fn test_rand_i64_in_range() {
-	min := i64(-5026245)
-	max := i64(209487239094)
-	for _ in 0 .. rnd_count {
-		value := rand.i64_in_range(min, max)
-		assert value >= min
-		assert value < max
-	}
-}
-
-fn test_rand_int31() {
-	for _ in 0 .. rnd_count {
-		value := rand.int31()
-		assert value >= 0
-		assert value <= math.max_i32
-	}
-}
-
-fn test_rand_int63() {
-	for _ in 0 .. rnd_count {
-		value := rand.int63()
-		assert value >= 0
-		assert value <= math.max_i64
-	}
-}
-
-fn test_rand_f32() {
-	for _ in 0 .. rnd_count {
-		value := rand.f32()
-		assert value >= 0.0
-		assert value < 1.0
-	}
-}
-
-fn test_rand_f64() {
-	for _ in 0 .. rnd_count {
-		value := rand.f64()
-		assert value >= 0.0
-		assert value < 1.0
-	}
-}
-
-fn test_rand_f32n() {
-	max := f32(34.52)
-	for _ in 0 .. rnd_count {
-		value := rand.f32n(max)
-		assert value >= 0.0
-		assert value < max
-	}
-}
-
-fn test_rand_f64n() {
-	max := 3495.2
-	for _ in 0 .. rnd_count {
-		value := rand.f64n(max)
-		assert value >= 0.0
-		assert value < max
-	}
-}
-
-fn test_rand_f32_in_range() {
-	min := f32(-10.4)
-	max := f32(43.2)
-	for _ in 0 .. rnd_count {
-		value := rand.f32_in_range(min, max)
-		assert value >= min
-		assert value < max
-	}
-}
-
-fn test_rand_f64_in_range() {
-	min := -10980.4
-	max := -2.0
-	for _ in 0 .. rnd_count {
-		value := rand.f64_in_range(min, max)
-		assert value >= min
-		assert value < max
-	}
-}
\ No newline at end of file
diff --git a/vlib/rand/splitmix64.v b/vlib/rand/splitmix64.v
index 5ad00cb577..4012f78dfe 100644
--- a/vlib/rand/splitmix64.v
+++ b/vlib/rand/splitmix64.v
@@ -135,7 +135,7 @@ pub fn (mut rng SplitMix64RNG) intn(max int) int {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return int(rng.u32n(max))
+	return int(rng.u32n(u32(max)))
 }
 
 // rng.i64n(max) returns a pseudorandom int that lies in [0, max)
@@ -145,7 +145,7 @@ pub fn (mut rng SplitMix64RNG) i64n(max i64) i64 {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return i64(rng.u64n(max))
+	return i64(rng.u64n(u64(max)))
 }
 
 // rng.int_in_range(min, max) returns a pseudorandom int that lies in [min, max)
diff --git a/vlib/rand/splitmix64_test.v b/vlib/rand/splitmix64_test.v
index 0099a1e403..f8da0be13c 100644
--- a/vlib/rand/splitmix64_test.v
+++ b/vlib/rand/splitmix64_test.v
@@ -63,7 +63,7 @@ fn test_splitmix64_variability() {
 	}
 }
 
-fn check_uniformity_u64(rng rand.SplitMix64RNG, range u64) {
+fn check_uniformity_u64(mut rng rand.SplitMix64RNG, range u64) {
 	range_f64 := f64(range)
 	expected_mean := range_f64 / 2.0
 	mut variance := 0.0
@@ -84,12 +84,12 @@ fn test_splitmix64_uniformity_u64() {
 		mut rng := rand.SplitMix64RNG{}
 		rng.seed(seed)
 		for range in ranges {
-			check_uniformity_u64(rng, range)
+			check_uniformity_u64(mut rng, u64(range))
 		}
 	}
 }
 
-fn check_uniformity_f64(rng rand.SplitMix64RNG) {
+fn check_uniformity_f64(mut rng rand.SplitMix64RNG) {
 	expected_mean := 0.5
 	mut variance := 0.0
 	for _ in 0 .. sample_size {
@@ -108,7 +108,7 @@ fn test_splitmix64_uniformity_f64() {
 	for seed in seeds {
 		mut rng := rand.SplitMix64RNG{}
 		rng.seed(seed)
-		check_uniformity_f64(rng)
+		check_uniformity_f64(mut rng)
 	}
 }
 
@@ -118,7 +118,7 @@ fn test_splitmix64_u32n() {
 		mut rng := rand.SplitMix64RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
-			value := rng.u32n(max)
+			value := rng.u32n(u32(max))
 			assert value >= 0
 			assert value < max
 		}
@@ -145,7 +145,7 @@ fn test_splitmix64_u32_in_range() {
 		mut rng := rand.SplitMix64RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
-			value := rng.u32_in_range(min, max)
+			value := rng.u32_in_range(u32(min), u32(max))
 			assert value >= min
 			assert value < max
 		}
@@ -200,7 +200,7 @@ fn test_splitmix64_int63() {
 fn test_splimix64_intn() {
 	max := 2525642
 	for seed in seeds {
-		rng := rand.SplitMix64RNG{}
+		mut rng := rand.SplitMix64RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.intn(max)
@@ -213,7 +213,7 @@ fn test_splimix64_intn() {
 fn test_splimix64_i64n() {
 	max := i64(3246727724653636)
 	for seed in seeds {
-		rng := rand.SplitMix64RNG{}
+		mut rng := rand.SplitMix64RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.i64n(max)
@@ -227,7 +227,7 @@ fn test_splimix64_int_in_range() {
 	min := -4252
 	max := 230549862
 	for seed in seeds {
-		rng := rand.SplitMix64RNG{}
+		mut rng := rand.SplitMix64RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.int_in_range(min, max)
@@ -241,7 +241,7 @@ fn test_splimix64_i64_in_range() {
 	min := i64(-24095)
 	max := i64(324058)
 	for seed in seeds {
-		rng := rand.SplitMix64RNG{}
+		mut rng := rand.SplitMix64RNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.i64_in_range(min, max)
diff --git a/vlib/rand/system_rng.c.v b/vlib/rand/system_rng.c.v
index f957458982..0561b9bb9f 100644
--- a/vlib/rand/system_rng.c.v
+++ b/vlib/rand/system_rng.c.v
@@ -204,7 +204,7 @@ pub fn (r SysRNG) intn(max int) int {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return int(r.u32n(max))
+	return int(r.u32n(u32(max)))
 }
 
 // r.i64n(max) returns a pseudorandom i64 that lies in [0, max)
@@ -214,7 +214,7 @@ pub fn (r SysRNG) i64n(max i64) i64 {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return i64(r.u64n(max))
+	return i64(r.u64n(u64(max)))
 }
 
 // r.int_in_range(min, max) returns a pseudorandom int that lies in [min, max)
diff --git a/vlib/rand/system_rng_test.v b/vlib/rand/system_rng_test.v
index bc4077fa5d..0309edf066 100644
--- a/vlib/rand/system_rng_test.v
+++ b/vlib/rand/system_rng_test.v
@@ -28,8 +28,8 @@ fn test_sys_rng_reproducibility() {
 	// seed for another batch of data.
 	for seed in seeds {
 		seed_data := [seed]
-		r1 := rand.SysRNG{}
-		r2 := rand.SysRNG{}
+		mut r1 := rand.SysRNG{}
+		mut r2 := rand.SysRNG{}
 		r1.seed(seed_data)
 		ints1 := get_n_randoms(value_count, r1)
 		r2.seed(seed_data)
@@ -55,7 +55,7 @@ fn test_sys_rng_variability() {
 	// improbable but not impossible.
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		mut values := []u64{cap: value_count}
 		for i in 0 .. value_count {
@@ -88,10 +88,10 @@ fn test_sys_rng_uniformity_u64() {
 	ranges := [14019545, 80240, 130]
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for range in ranges {
-			check_uniformity_u64(rng, range)
+			check_uniformity_u64(rng, u64(range))
 		}
 	}
 }
@@ -114,7 +114,7 @@ fn test_sys_rng_uniformity_f64() {
 	// The f64 version
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		check_uniformity_f64(rng)
 	}
@@ -124,10 +124,10 @@ fn test_sys_rng_u32n() {
 	max := 16384
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
-			value := rng.u32n(max)
+			value := rng.u32n(u32(max))
 			assert value >= 0
 			assert value < max
 		}
@@ -138,7 +138,7 @@ fn test_sys_rng_u64n() {
 	max := u64(379091181005)
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.u64n(max)
@@ -153,10 +153,10 @@ fn test_sys_rng_u32_in_range() {
 	min := 316846
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
-			value := rng.u32_in_range(min, max)
+			value := rng.u32_in_range(u32(min), u32(max))
 			assert value >= min
 			assert value < max
 		}
@@ -168,7 +168,7 @@ fn test_sys_rng_u64_in_range() {
 	min := u64(6848646868)
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.u64_in_range(min, max)
@@ -182,7 +182,7 @@ fn test_sys_rng_intn() {
 	max := 2525642
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.intn(max)
@@ -196,7 +196,7 @@ fn test_sys_rng_i64n() {
 	max := i64(3246727724653636)
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.i64n(max)
@@ -211,7 +211,7 @@ fn test_sys_rng_int_in_range() {
 	max := 23054962
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.int_in_range(min, max)
@@ -226,7 +226,7 @@ fn test_sys_rng_i64_in_range() {
 	max := i64(324058)
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.i64_in_range(min, max)
@@ -241,7 +241,7 @@ fn test_sys_rng_int31() {
 	sign_mask := 0x80000000
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.int31()
@@ -258,7 +258,7 @@ fn test_sys_rng_int63() {
 	sign_mask := i64(0x8000000000000000)
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.int63()
@@ -272,7 +272,7 @@ fn test_sys_rng_int63() {
 fn test_sys_rng_f32() {
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.f32()
@@ -285,7 +285,7 @@ fn test_sys_rng_f32() {
 fn test_sys_rng_f64() {
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.f64()
@@ -299,7 +299,7 @@ fn test_sys_rng_f32n() {
 	max := f32(357.0)
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.f32()
@@ -313,7 +313,7 @@ fn test_sys_rng_f64n() {
 	max := 1.52e6
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.f64()
@@ -328,7 +328,7 @@ fn test_sys_rng_f32_in_range() {
 	max := f32(125.0)
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.f32()
@@ -343,7 +343,7 @@ fn test_sys_rng_f64_in_range() {
 	max := 5015.2
 	for seed in seeds {
 		seed_data := [seed]
-		rng := rand.SysRNG{}
+		mut rng := rand.SysRNG{}
 		rng.seed(seed_data)
 		for _ in 0 .. range_limit {
 			value := rng.f64()
diff --git a/vlib/rand/wyrand.v b/vlib/rand/wyrand.v
index 3ec2263211..df682a7108 100644
--- a/vlib/rand/wyrand.v
+++ b/vlib/rand/wyrand.v
@@ -164,7 +164,7 @@ pub fn (mut rng WyRandRNG) intn(max int) int {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return int(rng.u32n(max))
+	return int(rng.u32n(u32(max)))
 }
 
 // rng.i64n(max) returns a pseudorandom int that lies in [0, max)
@@ -174,7 +174,7 @@ pub fn (mut rng WyRandRNG) i64n(max i64) i64 {
 		eprintln('max has to be positive.')
 		exit(1)
 	}
-	return i64(rng.u64n(max))
+	return i64(rng.u64n(u64(max)))
 }
 
 // rng.int_in_range(min, max) returns a pseudorandom int that lies in [min, max)
diff --git a/vlib/rand/wyrand_test.v b/vlib/rand/wyrand_test.v
index 20350023c0..2eaa1d3014 100644
--- a/vlib/rand/wyrand_test.v
+++ b/vlib/rand/wyrand_test.v
@@ -63,7 +63,7 @@ fn test_wyrand_variability() {
 	}
 }
 
-fn check_uniformity_u64(rng rand.WyRandRNG, range u64) {
+fn check_uniformity_u64(mut rng rand.WyRandRNG, range u64) {
 	range_f64 := f64(range)
 	expected_mean := range_f64 / 2.0
 	mut variance := 0.0
@@ -84,12 +84,12 @@ fn test_wyrand_uniformity_u64() {
 		mut rng := rand.WyRandRNG{}
 		rng.seed(seed)
 		for range in ranges {
-			check_uniformity_u64(rng, range)
+			check_uniformity_u64(mut rng, u64(range))
 		}
 	}
 }
 
-fn check_uniformity_f64(rng rand.WyRandRNG) {
+fn check_uniformity_f64(mut rng rand.WyRandRNG) {
 	expected_mean := 0.5
 	mut variance := 0.0
 	for _ in 0 .. sample_size {
@@ -108,7 +108,7 @@ fn test_wyrand_uniformity_f64() {
 	for seed in seeds {
 		mut rng := rand.WyRandRNG{}
 		rng.seed(seed)
-		check_uniformity_f64(rng)
+		check_uniformity_f64(mut rng)
 	}
 }
 
@@ -118,7 +118,7 @@ fn test_wyrand_u32n() {
 		mut rng := rand.WyRandRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
-			value := rng.u32n(max)
+			value := rng.u32n(u32(max))
 			assert value >= 0
 			assert value < max
 		}
@@ -145,7 +145,7 @@ fn test_wyrand_u32_in_range() {
 		mut rng := rand.WyRandRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
-			value := rng.u32_in_range(min, max)
+			value := rng.u32_in_range(u32(min), u32(max))
 			assert value >= min
 			assert value < max
 		}
@@ -200,7 +200,7 @@ fn test_wyrand_int63() {
 fn test_wyrand_intn() {
 	max := 2525642
 	for seed in seeds {
-		rng := rand.WyRandRNG{}
+		mut rng := rand.WyRandRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.intn(max)
@@ -213,7 +213,7 @@ fn test_wyrand_intn() {
 fn test_wyrand_i64n() {
 	max := i64(3246727724653636)
 	for seed in seeds {
-		rng := rand.WyRandRNG{}
+		mut rng := rand.WyRandRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.i64n(max)
@@ -227,7 +227,7 @@ fn test_wyrand_int_in_range() {
 	min := -4252
 	max := 1034
 	for seed in seeds {
-		rng := rand.WyRandRNG{}
+		mut rng := rand.WyRandRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.int_in_range(min, max)
@@ -241,7 +241,7 @@ fn test_wyrand_i64_in_range() {
 	min := i64(-24095)
 	max := i64(324058)
 	for seed in seeds {
-		rng := rand.WyRandRNG{}
+		mut rng := rand.WyRandRNG{}
 		rng.seed(seed)
 		for _ in 0 .. range_limit {
 			value := rng.i64_in_range(min, max)