diff --git a/pkgs/tools/misc/unclutter-xfixes/default.nix b/pkgs/tools/misc/unclutter-xfixes/default.nix
index 710932af5e9..d04846637a0 100644
--- a/pkgs/tools/misc/unclutter-xfixes/default.nix
+++ b/pkgs/tools/misc/unclutter-xfixes/default.nix
@@ -16,6 +16,9 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [ pkg-config asciidoc libxslt docbook_xsl ];
   buildInputs = [ xlibsWrapper libev libXi libXfixes ];
 
+  prePatch = ''
+    substituteInPlace Makefile --replace 'PKG_CONFIG =' 'PKG_CONFIG ?='
+  '';
   makeFlags = [ "CC=${stdenv.cc.targetPrefix}cc" ];
 
   installFlags = [ "PREFIX=$(out)" ];