diff -rup geom.orig/geom.h geom/geom.h
--- geom.orig/geom.h	Fri Jan 23 16:54:52 2004
+++ geom/geom.h	Mon Jan 26 00:34:48 2004
@@ -287,6 +287,10 @@ extern struct sx topology_lock;
 	};							\
 	DECLARE_MODULE(name, name##_mod, SI_SUB_DRIVERS, SI_ORDER_FIRST);
 
+#ifdef INVARIANTS
+boolean_t g_on_event_queue(void);
+#endif
+
 #endif /* _KERNEL */
 
 /* geom_ctl.c */
diff -rup geom.orig/geom_event.c geom/geom_event.c
--- geom.orig/geom_event.c	Fri Jan 23 16:54:52 2004
+++ geom/geom_event.c	Mon Jan 26 00:29:53 2004
@@ -312,7 +312,9 @@ g_waitfor_event(g_event_t *func, void *a
 
 	/* g_topology_assert_not(); */
 	KASSERT(flag == M_WAITOK || flag == M_NOWAIT,
-	    ("Wrong flag to g_post_event"));
+	    ("Wrong flag to g_waitfor_event"));
+	KASSERT(!g_on_event_queue(),
+	    ("Function g_waitfor_event called from the event queue"));
 	va_start(ap, flag);
 	error = g_post_event_x(func, arg, flag | EV_WAKEUP, &ep, ap);
 	va_end(ap);
diff -rup geom.orig/geom_kern.c geom/geom_kern.c
--- geom.orig/geom_kern.c	Fri Jan 23 16:54:52 2004
+++ geom/geom_kern.c	Mon Jan 26 00:35:20 2004
@@ -136,6 +136,18 @@ g_event_procbody(void)
 	}
 }
 
+#ifdef INVARIANTS
+/*
+ * Check if we're on the event queue.
+ */
+boolean_t
+g_on_event_queue(void)
+{
+
+	return (curthread->td_proc->p_pid == g_event_proc->p_pid);
+}
+#endif
+
 static struct kproc_desc g_event_kp = {
 	"g_event",
 	g_event_procbody,