diff --git a/pmap.go b/pmap.go
index 88ff72d..8d55b99 100644
--- a/pmap.go
+++ b/pmap.go
@@ -113,7 +113,7 @@ func (n *collision) getNode(hash uint32, key Key) interface{} {
 }
 
 func lookup(root interface{}, hash uint32, key Key, zero Value) (Value, bool) {
-	shift := 0
+	var shift uint32
 	cur := root
 	for {
 		switch n := cur.(type) {