diff --git a/setup.cfg b/setup.cfg
index 5cfd0321..a5234d1b 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -50,6 +50,7 @@ install_requires =
     email-validator
     ExifRead>=2.0.0
     Whoosh>=2.7.4  # for search
+    snowballstemmer>=1.1  # required by sphinx
     feedgenerator
     itsdangerous
     jinja2