diff --git a/requirements/base.in b/requirements/base.in
index b9ccf0ee7b9bb0c17a4fc765280f77c4e5fedf83..0c9a5aba3957704142543be5d1087a557406b484 100644
--- a/requirements/base.in
+++ b/requirements/base.in
@@ -29,3 +29,4 @@ fastjsonschema
 tweepy
 requests-cache
 wand
+tatsu<=5.8.3
diff --git a/requirements/base.txt b/requirements/base.txt
index f6535dabfaa23ac9d7377ccc37e759af884192c4..ac6ccd272b27e749a2199f88340e1a3fccf375e2 100644
--- a/requirements/base.txt
+++ b/requirements/base.txt
@@ -247,8 +247,10 @@ sqlparse==0.4.4
     # via django
 stack-data==0.6.3
     # via ipython
-tatsu==5.11.3
-    # via ics
+tatsu==5.8.3
+    # via
+    #   -r base.in
+    #   ics
 telepath==0.3.1
     # via wagtail
 tinycss2==1.2.1