--- kern/kern_timeout.c.orig	Sat Apr 21 21:19:22 2007
+++ kern/kern_timeout.c	Sat Apr 21 21:19:51 2007
@@ -289,7 +289,8 @@
 					lastfunc = c_func;
 				}
 #endif
-				if ((c_flags & CALLOUT_RETURNUNLOCKED) == 0)
+				if (c_mtx != NULL &&
+				    (c_flags & CALLOUT_RETURNUNLOCKED) == 0)
 					mtx_unlock(c_mtx);
 			skip:
 				mtx_lock_spin(&callout_lock);