diff --git a/src/Transport/Socket.php b/src/Transport/Socket.php
index 208f2463..fad3ae5c 100644
--- a/src/Transport/Socket.php
+++ b/src/Transport/Socket.php
@@ -81,7 +81,7 @@ public function request($method, UriInterface $uri, $data = null, array $headers
         }
 
         // Configure protocol version, use transport's default if not set otherwise.
-        $protocolVersion = $this->getOption('protocolVersion', '1.1');
+        $protocolVersion = $this->getOption('protocolVersion', '1.0');
 
         // Build the request payload.
         $request   = [];