diff --git a/src/WebSocketsServer.cpp b/src/WebSocketsServer.cpp
index 57e61e4..dbe0b34 100644
--- a/src/WebSocketsServer.cpp
+++ b/src/WebSocketsServer.cpp
@@ -590,7 +590,7 @@ void WebSocketsServer::handleHeader(WSclient_t * client, String * headerLine) {
             String headerValue = headerLine->substring(headerLine->indexOf(':') + 2);
 
             if(headerName.equalsIgnoreCase("Connection")) {
-                if(headerValue.indexOf("Upgrade") >= 0) {
+                if(headerValue.equalsIgnoreCase("Upgrade")) {
                     client->cIsUpgrade = true;
                 }
             } else if(headerName.equalsIgnoreCase("Upgrade")) {