diff --git a/src/WebSocketsClient.cpp b/src/WebSocketsClient.cpp
index 81e8a6d..9ed5d5c 100644
--- a/src/WebSocketsClient.cpp
+++ b/src/WebSocketsClient.cpp
@@ -319,10 +319,13 @@ void WebSocketsClient::handleHeader(WSclient_t * client) {
             client->cCode = headerLine.substring(9, headerLine.indexOf(' ', 9)).toInt();
         } else if(headerLine == "Connection: Upgrade") {
             client->cIsUpgrade = true;
-        } else if(headerLine == "Upgrade: websocket") {
-            client->cIsWebsocket = true;
-        } else if(headerLine == "Upgrade: WebSocket") {
-            client->cIsWebsocket = true;
+        } else if(headerLine.startsWith("Upgrade: ")) {
+            // 9 = lenght of "Upgrade: "
+            String low = headerLine.substring(9);
+            low.toLowerCase();
+            if(low == "websocket") {
+                client->cIsWebsocket = true;
+            }
         } else if(headerLine.startsWith("Sec-WebSocket-Accept: ")) {
             // 22 = lenght of "Sec-WebSocket-Accept: "
             client->cAccept = headerLine.substring(22);
diff --git a/src/WebSocketsServer.cpp b/src/WebSocketsServer.cpp
index c593dc3..cdabd2c 100644
--- a/src/WebSocketsServer.cpp
+++ b/src/WebSocketsServer.cpp
@@ -404,10 +404,13 @@ void WebSocketsServer::handleHeader(WSclient_t * client) {
             client->cUrl = headerLine.substring(4, headerLine.indexOf(' ', 4));
         } else if(headerLine == "Connection: Upgrade") {
             client->cIsUpgrade = true;
-        } else if(headerLine == "Upgrade: websocket") {
-            client->cIsWebsocket = true;
-        } else if(headerLine == "Upgrade: WebSocket") {
-            client->cIsWebsocket = true;
+        } else if(headerLine.startsWith("Upgrade: ")) {
+            // 9 = lenght of "Upgrade: "
+            String low = headerLine.substring(9);
+            low.toLowerCase();
+            if(low == "websocket") {
+                client->cIsWebsocket = true;
+            }
         } else if(headerLine.startsWith("Sec-WebSocket-Version: ")) {
             // 23 = lenght of "Sec-WebSocket-Version: "
             client->cVersion = headerLine.substring(23).toInt();