diff --git a/src/racket/src/thread.c b/src/racket/src/thread.c
index 7e77ba71b7..231ca2a059 100644
--- a/src/racket/src/thread.c
+++ b/src/racket/src/thread.c
@@ -6534,7 +6534,7 @@ static void escape_during_sync(Syncing *syncing)
 
   syncing->thread = NULL;
 
-  if (p->sync_box)
+  if (p && p->sync_box)
     scheme_post_sema_all(p->sync_box);
   scheme_post_syncing_nacks(syncing);