diff --git a/flake.nix b/flake.nix
index 5796c54ea..e3f8c728c 100644
--- a/flake.nix
+++ b/flake.nix
@@ -653,6 +653,7 @@
             inherit system crossSystem;
             overlays = [ self.overlays.default ];
           };
+          inherit (nixpkgsCross) lib;
         in with commonDeps { pkgs = nixpkgsCross; }; nixpkgsCross.stdenv.mkDerivation {
           name = "nix-${version}";
 
@@ -665,7 +666,11 @@
           nativeBuildInputs = nativeBuildDeps;
           buildInputs = buildDeps ++ propagatedDeps;
 
-          configureFlags = [ "--sysconfdir=/etc" "--disable-doc-gen" ];
+          configureFlags = [
+            "CXXFLAGS=-I${lib.getDev nixpkgsCross.rapidcheck}/extras/gtest/include"
+            "--sysconfdir=/etc"
+            "--disable-doc-gen"
+          ];
 
           enableParallelBuilding = true;