diff --git a/sys/kern/kern_physio.c b/sys/kern/kern_physio.c
index 5c63ab983390..e4851f967254 100644
--- a/sys/kern/kern_physio.c
+++ b/sys/kern/kern_physio.c
@@ -180,7 +180,7 @@ physio_biodone(struct buf *bp)
 	KASSERT(bp->b_bcount <= todo);
 	KASSERT(bp->b_resid <= bp->b_bcount);
 	if (done == todo)
-		KASSERT(bp->b_error == 0);
+		KASSERTMSG(bp->b_error == 0, "error=%d", bp->b_error);
 #endif /* defined(DIAGNOSTIC) */
 
 	workqueue_enqueue(physio_workqueue, &bp->b_work, NULL);