diff --git a/hardware/esp8266com/esp8266/cores/esp8266/WString.h b/hardware/esp8266com/esp8266/cores/esp8266/WString.h
index abba02f22..269b70291 100644
--- a/hardware/esp8266com/esp8266/cores/esp8266/WString.h
+++ b/hardware/esp8266com/esp8266/cores/esp8266/WString.h
@@ -32,6 +32,9 @@
 // result objects are assumed to be writable by subsequent concatenations.
 class StringSumHelper;
 
+typedef char* __FlashStringHelper;
+#define F(str) str
+
 // The string class
 class String
 {