---  sys/cam/cam_periph.c.orig
+++  sys/cam/cam_periph.c
@@ -325,8 +325,6 @@
 	struct mtx *mtx;
 	int error;
 
-	mtx_assert(periph->sim->mtx, MA_OWNED);
-
 	/*
 	 * Increment the reference count on the peripheral
 	 * while we wait for our lock attempt to succeed
@@ -338,6 +336,7 @@
 		return (ENXIO);
 
 	mtx = periph->sim->mtx;
+	mtx_assert(mtx, MA_OWNED);
 	if (mtx == &Giant)
 		mtx = NULL;