diff --git a/requirements.txt b/requirements.txt
index d3239f439..e6bdf7255 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -14,7 +14,7 @@ Markdown==3.8.1
 phpserialize==1.3.0 # phpserialize is only required during the migration
 psycopg2-binary==2.9.11
 pyjwt==2.14.0
-pymdown-extensions==11.0.1
+pymdown-extensions==10.21.3 # 11.0+ drops Python 3.9 support, which we still target
 pyproj==3.6.1
 pyramid_jwt==1.6.1
 pyramid==1.10.8