diff --git a/pkgs/development/python-modules/twisted/default.nix b/pkgs/development/python-modules/twisted/default.nix
index 1c91dfc2b48f..3b2c393b35b3 100644
--- a/pkgs/development/python-modules/twisted/default.nix
+++ b/pkgs/development/python-modules/twisted/default.nix
@@ -41,7 +41,9 @@ buildPythonPackage rec {
   # http://twistedmatrix.com/documents/current/core/howto/plugin.html#auto3
   # and http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=477103 for
   # details.
-  postInstall = "$out/bin/twistd --help > /dev/null";
+  postFixup = ''
+    $out/bin/twistd --help > /dev/null
+  '';
 
   checkPhase = ''
     ${python.interpreter} -m unittest discover -s twisted/test