diff --git a/folly/String.h b/folly/String.h
index 167a6b5..586dd8d 100644
--- a/folly/String.h
+++ b/folly/String.h
@@ -18,6 +18,7 @@
 #define FOLLY_BASE_STRING_H_
 
 #include <exception>
+#include <stdarg.h>
 #include <string>
 #include <boost/type_traits.hpp>