diff --git a/Source/SocketIO/Engine/SocketEngineWebsocket.swift b/Source/SocketIO/Engine/SocketEngineWebsocket.swift
index f0b209a..9a2a294 100644
--- a/Source/SocketIO/Engine/SocketEngineWebsocket.swift
+++ b/Source/SocketIO/Engine/SocketEngineWebsocket.swift
@@ -161,6 +161,8 @@ extension SocketEngineWebsocket {
 }
 
 #if os(Linux)
+protocol WebSocketDelegate { }
+
 /// SSLSecurity does nothing on Linux.
 public final class SSLSecurity { }