diff --git a/pkgs/development/libraries/webkitgtk/2.20.nix b/pkgs/development/libraries/webkitgtk/2.20.nix
index 8b44f11ee930..588f4bc4e3bd 100644
--- a/pkgs/development/libraries/webkitgtk/2.20.nix
+++ b/pkgs/development/libraries/webkitgtk/2.20.nix
@@ -39,6 +39,12 @@ stdenv.mkDerivation rec {
     patchShebangs .
   '';
 
+  postConfigure = ''
+    # A stopgap for a non-deterministic build failure when using only one core
+    # Upstream bug: https://bugs.webkit.org/show_bug.cgi?id=183788#c4
+    ninja JavaScriptCoreForwardingHeaders WTFForwardingHeaders
+  '';
+
   cmakeFlags = [
   "-DPORT=GTK"
   "-DUSE_LIBHYPHEN=0"