diff --git a/src/thread.c b/src/thread.c
index e2158019839..0cd1ae33dc2 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -645,10 +645,7 @@ mark_threads_callback (void *ignore)
       Lisp_Object thread_obj;
 
       XSETTHREAD (thread_obj, iter);
-      /* Don't mark main_thread, since it is not allocated
-	 dynamically, thus nothing would unmark it.  */
-      if (iter != &main_thread)
-	mark_object (thread_obj);
+      mark_object (thread_obj);
       mark_one_thread (iter);
     }
 }