Index: firmware/buflib.c
===================================================================
--- firmware/buflib.c	(revision 31336)
+++ firmware/buflib.c	(working copy)
@@ -195,6 +195,8 @@
 static bool
 move_block(struct buflib_context* ctx, union buflib_data* block, int shift)
 {
+    if (block->val <= 0)
+        return false;
     char* new_start;
     union buflib_data *new_block, *tmp = block[1].handle;
     struct buflib_callbacks *ops = block[2].ops;