diff --git a/pkgs/by-name/nn/nn/package.nix b/pkgs/by-name/nn/nn/package.nix
index 792890e5c422..72fa1e817abc 100644
--- a/pkgs/by-name/nn/nn/package.nix
+++ b/pkgs/by-name/nn/nn/package.nix
@@ -17,6 +17,11 @@ stdenv.mkDerivation (finalAttrs: {
 
   sourceRoot = "${finalAttrs.src.name}/nn";
 
+  # fixes:
+  # triangle.c: In function 'triangulate':
+  # triangle.c:15619:1: error: number of arguments doesn't match prototype
+  env.NIX_CFLAGS_COMPILE = "-std=gnu17";
+
   passthru.updateScript = unstableGitUpdater { };
 
   meta = {