diff --git a/pkgs/by-name/pr/pretalx/package.nix b/pkgs/by-name/pr/pretalx/package.nix
index f3582c1b7fb5..4674812339ae 100644
--- a/pkgs/by-name/pr/pretalx/package.nix
+++ b/pkgs/by-name/pr/pretalx/package.nix
@@ -96,6 +96,7 @@ python.pkgs.buildPythonApplication rec {
     "pillow"
     "python-dateutil"
     "reportlab"
+    "rules"
   ];
 
   propagatedBuildInputs = with python.pkgs; [