--- src/sys/vfs/hammer/hammer_undo.c	2008/07/16 18:30:59	1.19
+++ src/sys/vfs/hammer/hammer_undo.c	2008/07/18 00:19:53	1.20
@@ -138,6 +138,9 @@ again:
 		undo = hammer_bnew(hmp, next_offset, &error, &buffer);
 	else
 		undo = hammer_bread(hmp, next_offset, &error, &buffer);
+	if (error)
+		goto done;
+
 	hammer_modify_buffer(NULL, buffer, NULL, 0);
 
 	KKASSERT(undomap->next_offset == next_offset);
@@ -191,8 +194,8 @@ again:
 	undomap->next_offset += bytes;
 
 	hammer_modify_buffer_done(buffer);
+done:
 	hammer_modify_volume_done(root_volume);
-
 	hammer_unlock(&hmp->undo_lock);
 
 	if (buffer)