diff --git a/socks.py b/socks.py
index 83b1435..df124eb 100644
--- a/socks.py
+++ b/socks.py
@@ -677,7 +677,7 @@ def _negotiate_HTTP(self, dest_addr, dest_port):
         ]
 
         if username and password:
-            http_headers.append(b"Proxy-Authorization: basic "
+            http_headers.append(b"Proxy-Authorization: Basic "
                                 + b64encode(username + b":" + password))
 
         http_headers.append(b"\r\n")