diff --git a/requirements.txt b/requirements.txt
index 54f29a61f..b642a9bee 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -34,7 +34,7 @@ flask
 vllm>=0.4.1
 openpyxl
 # for ifeval
-nltk
+nltk==3.8.1
 langdetect
 immutabledict
 # for math evaluations