diff --git a/websocket/_abnf.py b/websocket/_abnf.py
index 70de786..d3a5e2e 100644
--- a/websocket/_abnf.py
+++ b/websocket/_abnf.py
@@ -110,7 +110,7 @@ class ABNF(object):
             raise WebSocketProtocolException("rsv is not implemented, yet")
 
         if self.opcode not in ABNF.OPCODES:
-            raise WebSocketProtocolException("Invalid opcode " + self.opcode)
+            raise WebSocketProtocolException("Invalid opcode " + str(self.opcode))
 
         if self.opcode == ABNF.OPCODE_PING and not self.fin:
             raise WebSocketProtocolException("Invalid ping frame.")
diff --git a/websocket/_core.py b/websocket/_core.py
index f2accb8..26c1c8b 100644
--- a/websocket/_core.py
+++ b/websocket/_core.py
@@ -944,7 +944,8 @@ class WebSocket(object):
                 raise
 
         if not bytes:
-            self.sock.close()
+            if self.sock:
+                self.sock.close()
             self.sock = None
             self.connected = False
             raise WebSocketConnectionClosedException()