diff --git a/src/gc.c b/src/gc.c
index 7b9f098b5..443b778d9 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -1287,12 +1287,13 @@ clear_all_old(mrb_state *mrb, mrb_gc *gc)
     /* finish the half baked GC */
     incremental_gc_finish(mrb, gc);
   }
-
-  /* Sweep the dead objects, then reset all the live objects
-   * (including all the old objects, of course) to white. */
-  gc->generational = FALSE;
-  prepare_incremental_sweep(mrb, gc);
-  incremental_gc_finish(mrb, gc);
+  else {
+    /* Sweep the dead objects, then reset all the live objects
+     * (including all the old objects, of course) to white. */
+    gc->generational = FALSE;
+    prepare_incremental_sweep(mrb, gc);
+    incremental_gc_finish(mrb, gc);
+  }
   gc->generational = origin_mode;
 
   /* The gray objects have already been painted as white */