diff --git a/pkgs/servers/geospatial/mapcache/default.nix b/pkgs/servers/geospatial/mapcache/default.nix
index e9ac6e834979..e4326e920ced 100644
--- a/pkgs/servers/geospatial/mapcache/default.nix
+++ b/pkgs/servers/geospatial/mapcache/default.nix
@@ -48,7 +48,7 @@ stdenv.mkDerivation rec {
     "-DAPACHE_MODULE_DIR=${placeholder "out"}/modules"
   ];
 
-  env.NIX_CFLAGS_COMPILE = "-std=c99";
+  env.NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-std=c99";
 
   meta = with lib; {
     description = "A server that implements tile caching to speed up access to WMS layers";