diff --git a/cores/esp8266/StreamString.h b/cores/esp8266/StreamString.h
index 264604f7a..be11669a7 100644
--- a/cores/esp8266/StreamString.h
+++ b/cores/esp8266/StreamString.h
@@ -24,6 +24,8 @@
 #define __STREAMSTRING_H
 
 #include <limits>
+#include <algorithm>
+#include "Stream.h"
 #include "WString.h"
 
 ///////////////////////////////////////////////////////////////