diff --git a/pkgs/by-name/uc/ucommon/package.nix b/pkgs/by-name/uc/ucommon/package.nix
index a4e623a24d81..1e5830224512 100644
--- a/pkgs/by-name/uc/ucommon/package.nix
+++ b/pkgs/by-name/uc/ucommon/package.nix
@@ -18,7 +18,7 @@ stdenv.mkDerivation (finalAttrs: {
   nativeBuildInputs = [ pkg-config ];
 
   # use C++14 Standard until error handling code gets updated upstream
-  CXXFLAGS = [ "-std=c++14" ];
+  env.CXXFLAGS = toString [ "-std=c++14" ];
 
   # disable flaky networking test
   postPatch = ''