diff --git a/Modules/threadmodule.c b/Modules/threadmodule.c
index 3614296..baf6673 100644
--- a/Modules/threadmodule.c
+++ b/Modules/threadmodule.c
@@ -25,6 +25,7 @@
 static void
 lock_dealloc(lockobject *self)
 {
+	assert(self->lock_lock);
 	/* Unlock the lock so it's safe to free it */
 	PyThread_acquire_lock(self->lock_lock, 0);
 	PyThread_release_lock(self->lock_lock);