diff --git a/pkgs/tools/audio/tts/default.nix b/pkgs/tools/audio/tts/default.nix
index 0072c8c26028..159d68feac0f 100644
--- a/pkgs/tools/audio/tts/default.nix
+++ b/pkgs/tools/audio/tts/default.nix
@@ -43,6 +43,7 @@ python.pkgs.buildPythonApplication rec {
 
   postPatch = let
     relaxedConstraints = [
+      "cython"
       "gruut"
       "librosa"
       "mecab-python3"