diff --git a/operator-length.go b/operator-length.go
index 04c6aad..1e91a2a 100644
--- a/operator-length.go
+++ b/operator-length.go
@@ -24,8 +24,8 @@ func evalLength(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	if IsList(childValue) {
-		list, _ := childValue.([]any)
-		v = int64(len(list))
+		ls, _ := childValue.(*ListType)
+		v = int64(len(*ls))
 	} else if IsString(childValue) {
 		s, _ := childValue.(string)
 		v = int64(len(s))