diff --git a/src/AsyncWebSocket.h b/src/AsyncWebSocket.h
index 1dd0e50..2a47a0d 100644
--- a/src/AsyncWebSocket.h
+++ b/src/AsyncWebSocket.h
@@ -31,6 +31,10 @@
 #endif
 #include <ESPAsyncWebServer.h>
 
+#ifdef ESP8266
+#include <Hash.h>
+#endif
+
 class AsyncWebSocket;
 class AsyncWebSocketResponse;
 class AsyncWebSocketClient;