diff --git a/vlib/builtin/int_test.v b/vlib/builtin/int_test.v
index 793986ae3b..f22d0b4ef7 100644
--- a/vlib/builtin/int_test.v
+++ b/vlib/builtin/int_test.v
@@ -148,21 +148,18 @@ fn test_num_separator() {
 	// int
 	assert 100_000_0 == 1000000
 	assert -2_23_4_6 == -22346
-	assert 230_ == 230
 
 	// bin
 	assert 0b0_11 == 3
 	assert -0b0_100 == -4
-	assert 0b010_ == 2
 
 	// oct
 	assert 0o1_73 == 123
 	assert -0o17_5 == -125
-	assert -0o175_ == -125
+	assert -0o175 == -125
 
 	// hex
 	assert 0xFF == 255
-	assert 0xFF_ == 255
 	assert 0xF_F == 255
 
 	// f32 or f64
diff --git a/vlib/v/scanner/scanner.v b/vlib/v/scanner/scanner.v
index 607180b95b..f36ef8c02f 100644
--- a/vlib/v/scanner/scanner.v
+++ b/vlib/v/scanner/scanner.v
@@ -338,6 +338,9 @@ fn (mut s Scanner) ident_bin_number() string {
 	}
 	for s.pos < s.text.len {
 		c := s.text[s.pos]
+		if c == num_sep && s.text[s.pos + 1] == num_sep {
+			s.error('cannot use `_` consecutively')
+		}
 		if !c.is_bin_digit() && c != num_sep {
 			if (!c.is_digit() && !c.is_letter()) || s.is_inside_string {
 				break
@@ -349,7 +352,10 @@ fn (mut s Scanner) ident_bin_number() string {
 		}
 		s.pos++
 	}
-	if start_pos + 2 == s.pos {
+	if s.text[s.pos - 1] == num_sep {
+		s.error('cannot use `_` at the end of a numeric literal')
+	}
+	else if start_pos + 2 == s.pos {
 		s.pos-- // adjust error position
 		s.error('number part of this binary is not provided')
 	} else if has_wrong_digit {
@@ -372,6 +378,9 @@ fn (mut s Scanner) ident_hex_number() string {
 	}
 	for s.pos < s.text.len {
 		c := s.text[s.pos]
+		if c == num_sep && s.text[s.pos + 1] == num_sep {
+			s.error('cannot use `_` consecutively')
+		}
 		if !c.is_hex_digit() && c != num_sep {
 			if !c.is_letter() || s.is_inside_string {
 				break
@@ -383,7 +392,10 @@ fn (mut s Scanner) ident_hex_number() string {
 		}
 		s.pos++
 	}
-	if start_pos + 2 == s.pos {
+	if s.text[s.pos - 1] == num_sep {
+		s.error('cannot use `_` at the end of a numeric literal')
+	}
+	else if start_pos + 2 == s.pos {
 		s.pos-- // adjust error position
 		s.error('number part of this hexadecimal is not provided')
 	} else if has_wrong_digit {
@@ -406,6 +418,9 @@ fn (mut s Scanner) ident_oct_number() string {
 	}
 	for s.pos < s.text.len {
 		c := s.text[s.pos]
+		if c == num_sep && s.text[s.pos + 1] == num_sep {
+			s.error('cannot use `_` consecutively')
+		}
 		if !c.is_oct_digit() && c != num_sep {
 			if (!c.is_digit() && !c.is_letter()) || s.is_inside_string {
 				break
@@ -417,7 +432,10 @@ fn (mut s Scanner) ident_oct_number() string {
 		}
 		s.pos++
 	}
-	if start_pos + 2 == s.pos {
+	if s.text[s.pos - 1] == num_sep {
+		s.error('cannot use `_` at the end of a numeric literal')
+	}
+	else if start_pos + 2 == s.pos {
 		s.pos-- // adjust error position
 		s.error('number part of this octal is not provided')
 	} else if has_wrong_digit {
@@ -437,6 +455,9 @@ fn (mut s Scanner) ident_dec_number() string {
 	// scan integer part
 	for s.pos < s.text.len {
 		c := s.text[s.pos]
+		if c == num_sep && s.text[s.pos + 1]  == num_sep {
+			s.error('cannot use `_` consecutively')
+		}
 		if !c.is_digit() && c != num_sep {
 			if !c.is_letter() || c in [`e`, `E`] || s.is_inside_string {
 				break
@@ -448,6 +469,9 @@ fn (mut s Scanner) ident_dec_number() string {
 		}
 		s.pos++
 	}
+	if s.text[s.pos - 1] == num_sep {
+		s.error('cannot use `_` at the end of a numeric literal')
+	}
 	mut call_method := false // true for, e.g., 5.str(), 5.5.str(), 5e5.str()
 	mut is_range := false // true for, e.g., 5..10
 	mut is_float_without_fraction := false // true for, e.g. 5.