diff --git a/src/math/bits.go b/src/math/bits.go
index c5cb93b1594..3716a411f4f 100644
--- a/src/math/bits.go
+++ b/src/math/bits.go
@@ -48,7 +48,12 @@ func IsInf(f float64, sign int) bool {
 	// To avoid the floating-point hardware, could use:
 	//	x := Float64bits(f);
 	//	return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
-	return sign >= 0 && f > MaxFloat64 || sign <= 0 && f < -MaxFloat64
+	if sign == 0 {
+		f = Abs(f)
+	} else if sign < 0 {
+		f = -f
+	}
+	return f > MaxFloat64
 }
 
 // normalize returns a normal number y and exponent exp