diff --git a/vlib/math/math.v b/vlib/math/math.v
index b69783261c..3f63b965ed 100644
--- a/vlib/math/math.v
+++ b/vlib/math/math.v
@@ -322,3 +322,8 @@ pub fn aprox_cos(a f64) f64 {
 	a8 := -1.8776444013090451e-5
 	return a0 + a * (a1 + a * (a2 + a * (a3 + a * (a4 + a * (a5 + a * (a6 + a * (a7 + a * a8)))))))
 }
+
+// copysign returns a value with the magnitude of x and the sign of y
+pub fn copysign(x, y f64) f64 {
+	return f64_from_bits((f64_bits(x) & ~sign_mask) | (f64_bits(y) & sign_mask))
+}
diff --git a/vlib/math/math_test.v b/vlib/math/math_test.v
index 7e2c01c22b..f869326ea7 100644
--- a/vlib/math/math_test.v
+++ b/vlib/math/math_test.v
@@ -62,3 +62,11 @@ fn test_mod() {
 	a %= 2
 	assert a == 0
 }
+
+fn test_copysign() {
+	assert copysign(5, -7) == -5.0
+	assert copysign(-5, 7) == 5.0
+	assert copysign(-5, -7) == -5.0
+	assert copysign(10, 0) == 10.0
+	assert copysign(10, 10) == 10.0
+}