diff --git a/pkgs/os-specific/windows/mcfgthreads/default.nix b/pkgs/os-specific/windows/mcfgthreads/default.nix
index 6c4cd171025..3f882557e50 100644
--- a/pkgs/os-specific/windows/mcfgthreads/default.nix
+++ b/pkgs/os-specific/windows/mcfgthreads/default.nix
@@ -18,6 +18,10 @@ stdenv.mkDerivation {
     rm -r "$sourceRoot/debug" "$sourceRoot/release"
   '';
 
+  postPatch = ''
+    substituteInPlace Makefile.am --replace '-Werror' ''
+  '';
+
   nativeBuildInputs = [
     autoreconfHook
   ];