diff --git a/pkgs/tools/X11/x2vnc/default.nix b/pkgs/tools/X11/x2vnc/default.nix
index bb8525d30916..8debbae2d385 100644
--- a/pkgs/tools/X11/x2vnc/default.nix
+++ b/pkgs/tools/X11/x2vnc/default.nix
@@ -9,9 +9,11 @@ stdenv.mkDerivation rec {
     sha256 = "00bh9j3m6snyd2fgnzhj5vlkj9ibh69gfny9bfzlxbnivb06s1yw";
   };
 
+  env.NIX_CFLAGS_COMPILE = "-std=gnu89";
+
   buildInputs = with xorg; [
-      libX11 xorgproto libXext libXrandr
-    ];
+    libX11 xorgproto libXext libXrandr
+  ];
 
   hardeningDisable = [ "format" ];