Small fix on mark_free()

src/block_header.c

@@ -82,7 +82,7 @@ void mark_free(allocator_t *allocator, void *ptr) {
 
     if(allocator->border_ptr != ptr) {
         next_block_header = (block_header_t *) ((char *) ptr + get_size(ptr));
-        next_block_header->previous_size &= (~ 0x1U);
+        next_block_header->previous_size &= (~ ((size_t) 0x1));
     }    
 }