diff --git a/pkgs/by-name/vg/vgm2x/package.nix b/pkgs/by-name/vg/vgm2x/package.nix
index 3afea59c59ac..cae08d43f195 100644
--- a/pkgs/by-name/vg/vgm2x/package.nix
+++ b/pkgs/by-name/vg/vgm2x/package.nix
@@ -22,6 +22,7 @@ stdenv.mkDerivation (finalAttrs: {
 
   postPatch = ''
     substituteInPlace Makefile \
+      --replace-fail 'CFLAGS=' 'CFLAGS=-std=gnu99 ' \
       --replace-fail 'pkg-config' "$PKG_CONFIG"
   '';