diff --git a/src/calibre/srv/tests/web_sockets.py b/src/calibre/srv/tests/web_sockets.py
index ad361de217..1d8ea22ebd 100644
--- a/src/calibre/srv/tests/web_sockets.py
+++ b/src/calibre/srv/tests/web_sockets.py
@@ -251,9 +251,16 @@ class WebSocketTest(BaseTest):
                         {'opcode':opcode, 'payload':'f1', 'fin':0}, {'opcode':opcode, 'payload':'f2'}
                     ], close_code=PROTOCOL_ERROR, send_close=False)
 
+                client = server.connect()
+                self.simple_test(client, [{'opcode':0, 'payload':b'non-continuation frame'}, 'some text'], close_code=PROTOCOL_ERROR, send_close=False)
+
             fragments = 'frag1 frag2'.split()
             client = server.connect()
             self.simple_test(client, [
                 {'opcode':TEXT, 'payload':fragments[0], 'fin':0}, {'opcode':TEXT, 'payload':fragments[1]}
             ], [''.join(fragments)])
 
+            client = server.connect()
+            self.simple_test(client, [
+                {'opcode':TEXT, 'payload':fragments[0], 'fin':0}, (PING, b'pong'), {'opcode':TEXT, 'payload':fragments[1]}
+            ], [(PONG, b'pong'), ''.join(fragments)])
diff --git a/src/calibre/srv/web_socket.py b/src/calibre/srv/web_socket.py
index b6d8f30f23..4f2bc6638d 100644
--- a/src/calibre/srv/web_socket.py
+++ b/src/calibre/srv/web_socket.py
@@ -316,6 +316,10 @@ class WebSocketConnection(HTTPConnection):
 
         message_starting = self.current_recv_opcode is None
         if message_starting:
+            if opcode == CONTINUATION:
+                self.log.error('Client sent continuation frame with no message to continue')
+                self.websocket_close(PROTOCOL_ERROR, 'Continuation frame without any message to continue')
+                return
             self.current_recv_opcode = opcode
         message_finished = frame_finished and is_final_frame_of_message
         if message_finished: