diff --git a/lib/websocket/driver/base.js b/lib/websocket/driver/base.js
index dd61457..e4a07e2 100644
--- a/lib/websocket/driver/base.js
+++ b/lib/websocket/driver/base.js
@@ -77,7 +77,9 @@ var instance = {
 
   start: function() {
     if (this.readyState !== 0) return false;
-    this._write(this._handshakeResponse());
+    var response = this._handshakeResponse();
+    if (!response) return false;
+    this._write(response);
     if (this._stage !== -1) this._open();
     return true;
   },
diff --git a/lib/websocket/driver/hybi.js b/lib/websocket/driver/hybi.js
index 38c77d1..eaab7bf 100644
--- a/lib/websocket/driver/hybi.js
+++ b/lib/websocket/driver/hybi.js
@@ -281,7 +281,12 @@ var instance = {
   },
 
   _handshakeResponse: function() {
-    var extensions = this._extensions.generateResponse(this._request.headers['sec-websocket-extensions']);
+    try {
+      var extensions = this._extensions.generateResponse(this._request.headers['sec-websocket-extensions']);
+    } catch (e) {
+      return this._fail('protocol_error', e.message);
+    }
+
     if (extensions) this._headers.set('Sec-WebSocket-Extensions', extensions);
 
     var start   = 'HTTP/1.1 101 Switching Protocols',
@@ -294,12 +299,12 @@ var instance = {
     delete this._frame;
     delete this._message;
 
-    var wasOpen = this.readyState < 2;
+    var sendCloseFrame = (this.readyState === 1);
     this.readyState = 2;
     this._stage = 5;
 
     this._extensions.close(function() {
-      if (wasOpen) this.frame(reason, 'close', code);
+      if (sendCloseFrame) this.frame(reason, 'close', code);
       this.readyState = 3;
       this.emit('close', new Base.CloseEvent(code, reason));
     }, this);
diff --git a/spec/websocket/driver/hybi_spec.js b/spec/websocket/driver/hybi_spec.js
index 537c436..f6beb50 100644
--- a/spec/websocket/driver/hybi_spec.js
+++ b/spec/websocket/driver/hybi_spec.js
@@ -79,6 +79,37 @@ test.describe("Hybi", function() { with(this) {
         }})
       }})
 
+      describe("with invalid extensions", function() { with(this) {
+        before(function() { with(this) {
+          request().headers["sec-websocket-extensions"] = "x-webkit- -frame"
+        }})
+
+        it("does not write a handshake", function() { with(this) {
+          expect(driver().io, "emit").exactly(0)
+          driver().start()
+        }})
+
+        it("does not trigger the onopen event", function() { with(this) {
+          driver().start()
+          assertEqual( false, open )
+        }})
+
+        it("triggers the onerror event", function() { with(this) {
+          driver().start()
+          assertEqual( "Invalid Sec-WebSocket-Extensions header: x-webkit- -frame", error.message )
+        }})
+
+        it("triggers the onclose event", function() { with(this) {
+          driver().start()
+          assertEqual( [1002, "Invalid Sec-WebSocket-Extensions header: x-webkit- -frame"], close )
+        }})
+
+        it("changes the state to closed", function() { with(this) {
+          driver().start()
+          assertEqual( "closed", driver().getState() )
+        }})
+      }})
+
       describe("with custom headers", function() { with(this) {
         before(function() { with(this) {
           driver().setHeader("Authorization", "Bearer WAT")