diff --git a/python/sglang/srt/utils/common.py b/python/sglang/srt/utils/common.py
index a09c5fc98..1ecc3e7f9 100644
--- a/python/sglang/srt/utils/common.py
+++ b/python/sglang/srt/utils/common.py
@@ -2080,7 +2080,7 @@ class MultiprocessingSerializer:
 
         if output_str:
             # Convert bytes to base64-encoded string
-            pybase64.b64encode(output).decode("utf-8")
+            output = pybase64.b64encode(output).decode("utf-8")
 
         return output