fix warning

1 files changed, 1 insertions, 1 deletions

diff --git a/src/gc.c b/src/gc.c
index f335345df..22d47c6fc 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -779,7 +779,7 @@ static void
 gc_mark_gray_list(mrb_state *mrb, struct RBasic **gray_list) {
   struct RBasic *obj;
 
-  while (obj = *gray_list) {
+  while ((obj = *gray_list)) {
     if (is_gray(obj)) {
       gc_mark_children(mrb, obj);
     }