diff --git a/lib/libwebsockets.c b/lib/libwebsockets.c
index ec71d799e..444357bc9 100644
--- a/lib/libwebsockets.c
+++ b/lib/libwebsockets.c
@@ -555,6 +555,9 @@ libwebsocket_service_fd(struct libwebsocket_context *context,
 	int okay = 0;
 	struct lws_tokens eff_buf;
 	int more = 1;
+	int ext_count = 0;
+	struct libwebsocket_extension *ext;
+
 #ifdef LWS_OPENSSL_SUPPORT
 	char ssl_err_buf[512];
 #endif
@@ -1119,8 +1122,47 @@ libwebsocket_service_fd(struct libwebsocket_context *context,
 		if (wsi->c_protocol)
 			p += sprintf(p, "Sec-WebSocket-Protocol: %s\x0d\x0a",
 							       wsi->c_protocol);
-		p += sprintf(p, "Sec-WebSocket-Version: %d\x0d\x0a",
-			wsi->ietf_spec_revision); 
+
+		/* tell the server what extensions we could support */
+
+		p += sprintf(p, "Sec-WebSocket-Extensions: ");
+
+		ext =context->extensions;
+		while (ext && ext->callback) {
+
+			n = 0;
+			n = context->protocols[0].callback(context, wsi,
+				LWS_CALLBACK_CLIENT_CONFIRM_EXTENSION_SUPPORTED,
+					wsi->user_space, (char *)ext->name, 0);
+
+			/*
+			 * zero return from callback means
+			 * go ahead and allow the extension,
+			 * it's what we get if the callback is
+			 * unhandled
+			 */
+
+			if (n) {
+				ext++;
+				continue;
+			}
+
+			/* apply it */
+			
+			if (ext_count)
+				*p++ = ',';
+			p += sprintf(p, ext->name);
+			ext_count++;
+
+			ext++;
+		}
+
+		p += sprintf(p, "\x0d\x0a");
+
+		if (wsi->ietf_spec_revision)
+			p += sprintf(p, "Sec-WebSocket-Version: %d\x0d\x0a",
+						       wsi->ietf_spec_revision); 
+
 		/* give userland a chance to append, eg, cookies */
 		
 		context->protocols[0].callback(context, wsi,
diff --git a/lib/libwebsockets.h b/lib/libwebsockets.h
index c5ca187cc..3b2c11a1f 100644
--- a/lib/libwebsockets.h
+++ b/lib/libwebsockets.h
@@ -64,6 +64,7 @@ enum libwebsocket_callback_reasons {
 	LWS_CALLBACK_OPENSSL_PERFORM_CLIENT_CERT_VERIFICATION,
 	LWS_CALLBACK_CLIENT_APPEND_HANDSHAKE_HEADER,
 	LWS_CALLBACK_CONFIRM_EXTENSION_OKAY,
+	LWS_CALLBACK_CLIENT_CONFIRM_EXTENSION_SUPPORTED,
 	/* external poll() management support */
 	LWS_CALLBACK_ADD_POLL_FD,
 	LWS_CALLBACK_DEL_POLL_FD,
@@ -334,6 +335,15 @@ struct libwebsocket_context;
  *		content during this callback might not be useful for anything.
  *		Notice this callback comes to protocols[0].
  *
+ *	LWS_CALLBACK_CLIENT_CONFIRM_EXTENSION_SUPPORTED:	When a client
+ *		connection is being prepared to start a handshake to a server,
+ *		each supported extension is checked with protocols[0] callback
+ *		with this reason, giving the user code a chance to suppress the
+ *		claim to support that extension by returning non-zero.  If
+ *		unhandled, by default 0 will be returned and the extension
+ *		support included in the header to the server.  Notice this
+ *		callback comes to protocols[0].
+ *
  *	The next four reasons are optional and only need taking care of if you
  * 	will be integrating libwebsockets sockets into an external polling
  * 	array.
diff --git a/libwebsockets-api-doc.html b/libwebsockets-api-doc.html
index 46933879c..a82383bc9 100644
--- a/libwebsockets-api-doc.html
+++ b/libwebsockets-api-doc.html
@@ -664,6 +664,17 @@ valid.  Note though at this time the ESTABLISHED callback hasn't
 happened yet so if you initialize <tt><b>user</b></tt> content there, <tt><b>user</b></tt>
 content during this callback might not be useful for anything.
 Notice this callback comes to protocols[0].
+</blockquote>
+<h3>LWS_CALLBACK_CLIENT_CONFIRM_EXTENSION_SUPPORTED</h3>
+<blockquote>
+When a client
+connection is being prepared to start a handshake to a server,
+each supported extension is checked with protocols[0] callback
+with this reason, giving the user code a chance to suppress the
+claim to support that extension by returning non-zero.  If
+unhandled, by default 0 will be returned and the extension
+support included in the header to the server.  Notice this
+callback comes to protocols[0].
 <p>
 The next four reasons are optional and only need taking care of if you
 will be integrating libwebsockets sockets into an external polling