diff --git a/src/gc.c b/src/gc.c
index 08a8771143536..a4e7e5b472359 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -2344,7 +2344,8 @@ mark: {
             if (gc_cblist_task_scanner) {
                 export_gc_state(ptls, &sp);
                 gc_invoke_callbacks(jl_gc_cb_task_scanner_t,
-                    gc_cblist_task_scanner, (ta, ta == ptls2->root_task));
+                    gc_cblist_task_scanner,
+                    (ta, ptls2 != NULL && ta == ptls2->root_task));
                 import_gc_state(ptls, &sp);
             }
 #ifdef COPY_STACKS