diff --git a/pkgs/by-name/mu/mup/package.nix b/pkgs/by-name/mu/mup/package.nix
index 280e8d9ec1ed..b8a1ec2e0d88 100644
--- a/pkgs/by-name/mu/mup/package.nix
+++ b/pkgs/by-name/mu/mup/package.nix
@@ -60,6 +60,10 @@ stdenv.mkDerivation {
       --replace-fail /usr/share/doc $out/share/doc
   '';
 
+  env = {
+    NIX_CFLAGS_COMPILE = "-std=gnu17";
+  };
+
   enableParallelBuilding = false; # Undeclared dependencies + https://stackoverflow.com/a/19822767/1687334 for prolog.ps.
 
   meta = {