diff --git a/paddlepalm/distribute/reader.py b/paddlepalm/distribute/reader.py
index 062c7c9472a0dad7b2059187d74cacc1808a528b..c9cd87a49e8669bc213a01ab51c488f64179abf5 100644
--- a/paddlepalm/distribute/reader.py
+++ b/paddlepalm/distribute/reader.py
@@ -125,6 +125,7 @@ def decode_fake(nums, mask, bs):
 
     n_f = len(mask) - n_t
     p1 = nums - (n_t-1) * bs
+    assert p1 % (n_f+1) == 0
     each_f = p1 // (n_f+1)
     return each_f * n_f