Index: uspace/lib/block/libblock.c
===================================================================
--- uspace/lib/block/libblock.c	(revision 0dfaa099a12cf0db2564585eada36845dc3a6e97)
+++ uspace/lib/block/libblock.c	(revision 0f1cf7a31b3863c9e813511f9a942482d21348fd)
@@ -566,4 +566,5 @@
 	assert(devcon);
 	assert(devcon->cache);
+	assert(block->refcnt >= 1);
 
 	cache = devcon->cache;