diff --git a/pkgs/by-name/un/unrtf/package.nix b/pkgs/by-name/un/unrtf/package.nix
index ec986657c241..0657563f8012 100644
--- a/pkgs/by-name/un/unrtf/package.nix
+++ b/pkgs/by-name/un/unrtf/package.nix
@@ -11,6 +11,8 @@ stdenv.mkDerivation rec {
   pname = "unrtf";
   version = "0.21.10";
 
+  env.NIX_CFLAGS_COMPILE = "-std=gnu17";
+
   src = fetchurl {
     url = "https://ftp.gnu.org/gnu/${pname}/${pname}-${version}.tar.gz";
     sha256 = "1bil6z4niydz9gqm2j861dkxmqnpc8m7hvidsjbzz7x63whj17xl";