diff --git a/pkgs/development/libraries/python-qt/default.nix b/pkgs/development/libraries/python-qt/default.nix
index 43cf3254fc7d..7fa35a5b09ef 100644
--- a/pkgs/development/libraries/python-qt/default.nix
+++ b/pkgs/development/libraries/python-qt/default.nix
@@ -60,7 +60,7 @@ stdenv.mkDerivation (finalAttrs: {
     cp -r ./extensions $out/include/PythonQt
   '';
 
-  postFixup = lib.optionalString stdenv.isDarwin ''
+  preFixup = lib.optionalString stdenv.isDarwin ''
     install_name_tool -id \
       $out/lib/libPythonQt-Qt5-Python3.${python3.sourceVersion.minor}.dylib \
       $out/lib/libPythonQt-Qt5-Python3.${python3.sourceVersion.minor}.dylib