diff --git a/pkgs/by-name/gi/git-crypt/package.nix b/pkgs/by-name/gi/git-crypt/package.nix
index 46ff7e4602d2..aeb5635f37a4 100644
--- a/pkgs/by-name/gi/git-crypt/package.nix
+++ b/pkgs/by-name/gi/git-crypt/package.nix
@@ -42,7 +42,7 @@ stdenv.mkDerivation (finalAttrs: {
   ];
 
   # https://github.com/AGWA/git-crypt/issues/232
-  CXXFLAGS = [
+  env.CXXFLAGS = toString [
     "-DOPENSSL_API_COMPAT=0x30000000L"
   ];