diff --git a/pkgs/development/compilers/llvm/4/clang/default.nix b/pkgs/development/compilers/llvm/4/clang/default.nix
index a2ba1fe7f4c..77863ab4f1e 100644
--- a/pkgs/development/compilers/llvm/4/clang/default.nix
+++ b/pkgs/development/compilers/llvm/4/clang/default.nix
@@ -37,9 +37,6 @@ let
 
     patches = [ ./purity.patch ];
 
-    # XXX: TODO: This should be removed on next rebuild
-    postBuild = "";
-
     postPatch = ''
       sed -i -e 's/Args.hasArg(options::OPT_nostdlibinc)/true/' lib/Driver/Tools.cpp
       sed -i -e 's/DriverArgs.hasArg(options::OPT_nostdlibinc)/true/' lib/Driver/ToolChains.cpp
diff --git a/pkgs/development/compilers/llvm/5/clang/default.nix b/pkgs/development/compilers/llvm/5/clang/default.nix
index 0ee1404484b..c8eafce4e39 100644
--- a/pkgs/development/compilers/llvm/5/clang/default.nix
+++ b/pkgs/development/compilers/llvm/5/clang/default.nix
@@ -37,9 +37,6 @@ let
 
     patches = [ ./purity.patch ];
 
-    # XXX: TODO: This should be removed on next rebuild
-    postBuild = "";
-
     postPatch = ''
       sed -i -e 's/DriverArgs.hasArg(options::OPT_nostdlibinc)/true/' \
              -e 's/Args.hasArg(options::OPT_nostdlibinc)/true/' \