diff --git a/pkgs/development/libraries/kde-frameworks/default.nix b/pkgs/development/libraries/kde-frameworks/default.nix
index 845c911789d..9e03965441e 100644
--- a/pkgs/development/libraries/kde-frameworks/default.nix
+++ b/pkgs/development/libraries/kde-frameworks/default.nix
@@ -48,7 +48,7 @@ let
                     # Propagate $dev so that this setup hook is propagated
                     # But only if there is a separate $dev output
                     if [ "''${outputDev:?}" != out ]; then
-                        propagatedBuildInputs="$propagatedBuildInputs @dev@"
+                        propagatedBuildInputs="''${propagatedBuildInputs-} @dev@"
                     fi
                 fi
               '';