Index: uspace/srv/devmap/devmap.c
===================================================================
--- uspace/srv/devmap/devmap.c	(revision 66bea2437bb9d02ffae938d02247f34e80b03f21)
+++ uspace/srv/devmap/devmap.c	(revision c3f95d86d42c889ae39c8bc299b33beb8dbc4302)
@@ -123,4 +123,10 @@
 static devmap_handle_t last_handle = 0;
 static devmap_device_t *null_devices[NULL_DEVICES];
+
+/*
+ * Dummy list for null devices. This is necessary so that null devices can
+ * be used just as any other devices, e.g. in devmap_device_unregister_core().
+ */
+static LIST_INITIALIZE(dummy_null_driver_devices);
 
 static devmap_handle_t devmap_create_handle(void)
@@ -953,7 +959,11 @@
 	device->name = dev_name;
 	
-	/* Insert device into list of all devices
-	   and into null devices array */
+	/*
+	 * Insert device into list of all devices and into null devices array.
+	 * Insert device into a dummy list of null driver's devices so that it
+	 * can be safely removed later.
+	 */
 	list_append(&device->devices, &devices_list);
+	list_append(&device->driver_devices, &dummy_null_driver_devices);
 	null_devices[i] = device;
 	
Index: uspace/srv/fs/fat/fat_ops.c
===================================================================
--- uspace/srv/fs/fat/fat_ops.c	(revision 66bea2437bb9d02ffae938d02247f34e80b03f21)
+++ uspace/srv/fs/fat/fat_ops.c	(revision c3f95d86d42c889ae39c8bc299b33beb8dbc4302)
@@ -325,4 +325,5 @@
 		    uint16_t_le2host(d->firstc));
 		if (rc != EOK) {
+			(void) block_put(b);
 			(void) fat_node_put(FS_NODE(nodep));
 			return rc;
@@ -811,4 +812,5 @@
 	fibril_mutex_unlock(&childp->idx->lock);
 	childp->lnkcnt = 0;
+	childp->refcnt++;	/* keep the node in memory until destroyed */
 	childp->dirty = true;
 	fibril_mutex_unlock(&childp->lock);
@@ -1488,4 +1490,5 @@
 	fs_index_t index = (fs_index_t)IPC_GET_ARG2(*request);
 	fs_node_t *fn;
+	fat_node_t *nodep;
 	int rc;
 
@@ -1499,4 +1502,11 @@
 		return;
 	}
+
+	nodep = FAT_NODE(fn);
+	/*
+	 * We should have exactly two references. One for the above
+	 * call to fat_node_get() and one from fat_unlink().
+	 */
+	assert(nodep->refcnt == 2);
 
 	rc = fat_destroy_node(fn);