diff --git a/memide.c b/memide.c
index 38be9a4..63f0a24 100644
--- a/memide.c
+++ b/memide.c
@@ -39,8 +39,8 @@ iderw(struct buf *b)
 {
   uchar *p;
 
-  if(!(b->flags & B_BUSY))
-    panic("iderw: buf not busy");
+  if(!holdingsleep(&b->lock))
+    panic("iderw: buf not locked");
   if((b->flags & (B_VALID|B_DIRTY)) == B_VALID)
     panic("iderw: nothing to do");
   if(b->dev != 1)