diff --git a/operator-length.go b/operator-length.go
index 2467407..e699c64 100644
--- a/operator-length.go
+++ b/operator-length.go
@@ -25,12 +25,12 @@ func evalLength(ctx ExprContext, self *term) (v any, err error) {
 
 	if isList(rightValue) {
 		list, _ := rightValue.([]any)
-		v = len(list)
+		v = int64(len(list))
 	} else if isString(rightValue) {
 		s, _ := rightValue.(string)
-		v = len(s)
+		v = int64(len(s))
 	} else if it, ok := rightValue.(Iterator); ok {
-		v = it.Index()
+		v = int64(it.Index())
 	} else {
 		err = self.errIncompatibleType(rightValue)
 	}