diff --git a/requirements/requirements.txt b/requirements/requirements.txt
index 6622e2d49..163daaab2 100644
--- a/requirements/requirements.txt
+++ b/requirements/requirements.txt
@@ -1,4 +1,4 @@
-cdifflib
+cdifflib==1.2.6  # versions 1.2.7 and 1.2.8 use deprecated `ext-modules`
 editdistance
 inflect
 joblib