diff --git a/pkgs/by-name/ol/olsrd/package.nix b/pkgs/by-name/ol/olsrd/package.nix
index 8ba2a5e9ea70..8d46263b6814 100644
--- a/pkgs/by-name/ol/olsrd/package.nix
+++ b/pkgs/by-name/ol/olsrd/package.nix
@@ -27,6 +27,9 @@ stdenv.mkDerivation (finalAttrs: {
     })
   ];
 
+  # boolean type guards in olsr_types.h are incompatible with C23
+  env.NIX_CFLAGS_COMPILE = "-std=gnu17";
+
   buildInputs = [
     bison
     flex