diff --git a/pkgs/applications/audio/carla/default.nix b/pkgs/applications/audio/carla/default.nix
index a4b68707ee7c..500bbc81d38f 100644
--- a/pkgs/applications/audio/carla/default.nix
+++ b/pkgs/applications/audio/carla/default.nix
@@ -34,11 +34,12 @@ stdenv.mkDerivation rec {
 
   buildInputs = [
     file liblo alsaLib fluidsynth ffmpeg_3 jack2 libpulseaudio libsndfile
-  ] ++ pythonPath
-    ++ optional withQt qtbase
+  ] ++ optional withQt qtbase
     ++ optional withGtk2 gtk2
     ++ optional withGtk3 gtk3;
 
+  propagatedBuildInputs = pythonPath;
+
   enableParallelBuilding = true;
 
   installFlags = [ "PREFIX=$(out)" ];