diff --git a/pkgs/applications/version-management/monotone/default.nix b/pkgs/applications/version-management/monotone/default.nix
index 7a4fdb9d0811..d72a5d37a394 100644
--- a/pkgs/applications/version-management/monotone/default.nix
+++ b/pkgs/applications/version-management/monotone/default.nix
@@ -71,7 +71,7 @@ stdenv.mkDerivation rec {
       {} +
   '';
 
-  CXXFLAGS = " --std=c++11 ";
+  env.CXXFLAGS = " --std=c++11 ";
 
   nativeBuildInputs = [
     pkg-config