diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index f4b21d7..95b609d 100644
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -313,7 +313,7 @@
 		}
 
 		if (!(map.m_flags & EROFS_MAP_MAPPED)) {
-			memset(buffer + end - offset, 0, length);
+			memset(buffer + end - offset, 0, length - skip);
 			end = map.m_la;
 			continue;
 		}