diff --git a/libsparse/backed_block.c b/libsparse/backed_block.c
index 3e72b57..794cd6b 100644
--- a/libsparse/backed_block.c
+++ b/libsparse/backed_block.c
@@ -221,7 +221,8 @@
 		}
 		break;
 	case BACKED_BLOCK_FILE:
-		if (a->file.filename != b->file.filename ||
+		/* Already make sure b->type is BACKED_BLOCK_FILE */
+		if (strcmp(a->file.filename, b->file.filename) ||
 				a->file.offset + a->len != b->file.offset) {
 			return -EINVAL;
 		}
@@ -279,7 +280,10 @@
 	}
 
 	merge_bb(bbl, new_bb, new_bb->next);
-	merge_bb(bbl, bb, new_bb);
+	if (!merge_bb(bbl, bb, new_bb)) {
+		/* new_bb destroyed, point to retained as last_used */
+		bbl->last_used = bb;
+	}
 
 	return 0;
 }