diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/read_worker.cpp b/fs_mgr/libsnapshot/snapuserd/user-space-merge/read_worker.cpp
index 7268fca..7d2e3a6 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/read_worker.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/read_worker.cpp
@@ -305,7 +305,7 @@
                     return false;
                 }
 
-                ret = BLOCK_SZ;
+                ret = std::min(BLOCK_SZ, read_size);
             }
 
             read_size -= ret;