diff --git a/pkgs/development/python-modules/cld2-cffi/default.nix b/pkgs/development/python-modules/cld2-cffi/default.nix
index c54b962a8f6..a38d4c0866e 100644
--- a/pkgs/development/python-modules/cld2-cffi/default.nix
+++ b/pkgs/development/python-modules/cld2-cffi/default.nix
@@ -13,7 +13,7 @@ buildPythonPackage rec {
   checkInputs = [ nose ];
 
   # gcc doesn't approve of this code, so disable -Werror
-  NIX_CFLAGS_COMPILE = "-w";
+  NIX_CFLAGS_COMPILE = [ "-w" ] ++ stdenv.lib.optional stdenv.cc.isClang "-Wno-error=c++11-narrowing";
 
   checkPhase = "nosetests -v";