diff --git a/pkgs/applications/video/gnash/default.nix b/pkgs/applications/video/gnash/default.nix
index 4f2addcc99b..616b474393c 100644
--- a/pkgs/applications/video/gnash/default.nix
+++ b/pkgs/applications/video/gnash/default.nix
@@ -73,6 +73,8 @@ stdenv.mkDerivation rec {
        echo "\$GST_PLUGIN_PATH set to \`$GST_PLUGIN_PATH'"
     '';
 
+  postConfigure = "echo '#define nullptr NULL' >> gnashconfig.h";
+
   # Make sure `gtk-gnash' gets `libXext' in its `RPATH'.
   NIX_LDFLAGS="-lX11 -lXext";