diff --git a/pkgs/development/interpreters/spidermonkey/31.5.nix b/pkgs/development/interpreters/spidermonkey/31.5.nix
index 4ee6658f59c..3943de2d8f9 100644
--- a/pkgs/development/interpreters/spidermonkey/31.5.nix
+++ b/pkgs/development/interpreters/spidermonkey/31.5.nix
@@ -18,6 +18,7 @@ stdenv.mkDerivation rec {
   postUnpack = "sourceRoot=\${sourceRoot}/js/src";
 
   preConfigure = ''
+    export CXXFLAGS="-fpermissive"
     export LIBXUL_DIST=$out
   '';