diff --git a/lang/types/util.go b/lang/types/util.go
index 24140fdc..225f1506 100644
--- a/lang/types/util.go
+++ b/lang/types/util.go
@@ -23,13 +23,14 @@ import (
 )
 
 // nextPowerOfTwo gets the lowest number higher than v that is a power of two.
-func nextPowerOfTwo(v uint32) uint32 {
+func nextPowerOfTwo(v uint) uint {
 	v--
 	v |= v >> 1
 	v |= v >> 2
 	v |= v >> 4
 	v |= v >> 8
 	v |= v >> 16
+	v |= v >> 32
 	v++
 	return v
 }
diff --git a/lang/types/util_test.go b/lang/types/util_test.go
index 152051f4..7e64c3c5 100644
--- a/lang/types/util_test.go
+++ b/lang/types/util_test.go
@@ -20,7 +20,7 @@ package types
 import "testing"
 
 func TestNextPowerOfTwo(t *testing.T) {
-	testCases := map[uint32]uint32{
+	testCases := map[uint]uint{
 		1: 1,
 		2: 2,
 		3: 4,
diff --git a/lang/types/value.go b/lang/types/value.go
index a2077118..4dc7c958 100644
--- a/lang/types/value.go
+++ b/lang/types/value.go
@@ -333,7 +333,7 @@ func Into(v Value, rv reflect.Value) error {
 
 		switch kind {
 		case reflect.Slice:
-			pow := nextPowerOfTwo(uint32(count))
+			pow := nextPowerOfTwo(uint(count))
 			nval := reflect.MakeSlice(rv.Type(), count, int(pow))
 			rv.Set(nval)