diff --git a/cc/config/global.go b/cc/config/global.go
index 06f6f9a..c734c2e 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -170,6 +170,8 @@
 	pctx.StaticVariable("CommonClangGlobalCppflags",
 		strings.Join(append(ClangFilterUnknownCflags(commonGlobalCppflags), "${ClangExtraCppflags}"), " "))
 
+	pctx.StaticVariable("ClangExternalCflags", "${ClangExtraExternalCflags}")
+
 	// Everything in these lists is a crime against abstraction and dependency tracking.
 	// Do not add anything to this list.
 	pctx.PrefixedExistentPathsForSourcesVariable("CommonGlobalIncludes", "-I",