diff --git a/pkgs/by-name/li/libe57format/package.nix b/pkgs/by-name/li/libe57format/package.nix
index fe9d3bc5cbb2..892083d77d6a 100644
--- a/pkgs/by-name/li/libe57format/package.nix
+++ b/pkgs/by-name/li/libe57format/package.nix
@@ -27,7 +27,7 @@ stdenv.mkDerivation (finalAttrs: {
     hash = "sha256-JARpxp6Z2VioBfY0pZSyQU2mG/EllbaF3qteSFM9u8o=";
   };
 
-  CXXFLAGS = [
+  env.CXXFLAGS = toString [
     # GCC 13: error: 'int16_t' has not been declared in 'std'
     "-include cstdint"
   ];