diff --git a/src/math/bits/bits.go b/src/math/bits/bits.go
index 6ca4bfe9a6..c1c7b7978a 100644
--- a/src/math/bits/bits.go
+++ b/src/math/bits/bits.go
@@ -516,10 +516,6 @@ func Div32(hi, lo, y uint32) (quo, rem uint32) {
 // half in parameter hi and the lower half in parameter lo.
 // Div64 panics for y == 0 (division by zero) or y <= hi (quotient overflow).
 func Div64(hi, lo, y uint64) (quo, rem uint64) {
-	const (
-		two32  = 1 << 32
-		mask32 = two32 - 1
-	)
 	if y == 0 {
 		panic(divideError)
 	}
@@ -527,9 +523,18 @@ func Div64(hi, lo, y uint64) (quo, rem uint64) {
 		panic(overflowError)
 	}
 
+	// If high part is zero, we can directly return the results.
+	if hi == 0 {
+		return lo / y, lo % y
+	}
+
 	s := uint(LeadingZeros64(y))
 	y <<= s
 
+	const (
+		two32  = 1 << 32
+		mask32 = two32 - 1
+	)
 	yn1 := y >> 32
 	yn0 := y & mask32
 	un32 := hi<<s | lo>>(64-s)