diff --git a/pkgs/servers/geospatial/mapcache/default.nix b/pkgs/servers/geospatial/mapcache/default.nix
index eea321abb22..781edfce98c 100644
--- a/pkgs/servers/geospatial/mapcache/default.nix
+++ b/pkgs/servers/geospatial/mapcache/default.nix
@@ -48,6 +48,8 @@ stdenv.mkDerivation rec {
     "-DAPACHE_MODULE_DIR=${placeholder "out"}/modules"
   ];
 
+  NIX_CFLAGS_COMPILE = "-std=c99";
+
   meta = with lib; {
     description = "A server that implements tile caching to speed up access to WMS layers";
     homepage = "https://mapserver.org/mapcache/";