diff --git a/python/sglang/srt/disaggregation/decode.py b/python/sglang/srt/disaggregation/decode.py
index b58f713a1..f4ef07e41 100644
--- a/python/sglang/srt/disaggregation/decode.py
+++ b/python/sglang/srt/disaggregation/decode.py
@@ -690,7 +690,7 @@ class DecodePreallocQueue:
 
         # populate metadata
         req.fill_ids = req.origin_input_ids + req.output_ids
-        req.extend_input_len = len(req.origin_input_ids)
+        req.extend_input_len = len(req.fill_ids)
 
         return kv_loc