diff --git a/saltyrtc/server/message.py b/saltyrtc/server/message.py
index ff83094..72a55b7 100644
--- a/saltyrtc/server/message.py
+++ b/saltyrtc/server/message.py
@@ -220,6 +220,7 @@ def unpack(cls, client, data):
 
         # Decrypt if directed at us and keys have been exchanged
         # or just return a raw message to be sent to another client
+        expect_type = None
         if destination_type == AddressType.server:
             data = data[NONCE_LENGTH:]
             if not client.authenticated and client.type is None:
@@ -231,6 +232,8 @@ def unpack(cls, client, data):
                         cls._decrypt_payload(client, nonce, data))
                 except MessageError:
                     pass
+                else:
+                    expect_type = MessageType.client_auth
 
                 # Try client-hello (unencrypted)
                 if payload is None:
@@ -238,9 +241,11 @@ def unpack(cls, client, data):
                         payload = cls._unpack_payload(data)
                     except MessageError:
                         payload = None
+                    else:
+                        expect_type = MessageType.client_hello
 
                 # Still no payload?
-                if payload is None:
+                if expect_type is None or payload is None:
                     message = 'Expected either client-hello or client-auth, got neither'
                     raise MessageError(message)
             else:
@@ -266,6 +271,10 @@ def unpack(cls, client, data):
         except ValueError as exc:
             raise MessageError('Unknown message type: {}'.format(type_)) from exc
 
+        # Ensure type isn't violated
+        if expect_type is not None and type_ != expect_type:
+            raise MessageError('Expected type {}, got {}'.format(expect_type, type_))
+
         # Check and convert payload on appropriate message class
         try:
             message_class = cls._get_message_classes()[type_]
diff --git a/tests/test_protocol.py b/tests/test_protocol.py
index 7d64758..8eecdb1 100644
--- a/tests/test_protocol.py
+++ b/tests/test_protocol.py
@@ -354,6 +354,33 @@ def test_subprotocol_downgrade_2(
         assert not client.ws_client.open
         assert client.ws_client.close_code == CloseCode.protocol_error
 
+    @pytest.mark.asyncio
+    def test_initiator_handshake_unencrypted(
+            self, cookie_factory, pack_nonce, server, client_factory
+    ):
+        """
+        Check that we cannot do a complete handshake for an initiator
+        when 'client-auth' is not encrypted.
+        """
+        client = yield from client_factory()
+
+        # server-hello, already checked in another test
+        message, _, sck, s, d, start_scsn = yield from client.recv()
+
+        # client-auth
+        cck, ccsn = cookie_factory(), 2**32 - 1
+        yield from client.send(pack_nonce(cck, 0x00, 0x00, ccsn), {
+            'type': 'client-auth',
+            'your_cookie': sck,
+            'subprotocols': pytest.saltyrtc.subprotocols,
+        })
+        ccsn += 1
+
+        # Expect protocol error
+        yield from server.wait_connections_closed()
+        assert not client.ws_client.open
+        assert client.ws_client.close_code == CloseCode.protocol_error
+
     @pytest.mark.asyncio
     def test_initiator_handshake(
             self, cookie_factory, initiator_key, pack_nonce, server, client_factory,
@@ -447,6 +474,39 @@ def test_responder_handshake(
         yield from client.close()
         yield from server.wait_connections_closed()
 
+    @pytest.mark.asyncio
+    def test_responder_handshake_unencrypted(
+            self, cookie_factory, responder_key, pack_nonce, client_factory, server
+    ):
+        """
+        Check that we can do a complete handshake for a responder.
+        """
+        client = yield from client_factory()
+
+        # server-hello, already checked in another test
+        message, _, sck, s, d, start_scsn = yield from client.recv()
+
+        # client-hello
+        cck, ccsn = cookie_factory(), 2**32 - 1
+        yield from client.send(pack_nonce(cck, 0x00, 0x00, ccsn), {
+            'type': 'client-hello',
+            'key': responder_key.pk,
+        })
+        ccsn += 1
+
+        # client-auth
+        yield from client.send(pack_nonce(cck, 0x00, 0x00, ccsn), {
+            'type': 'client-auth',
+            'your_cookie': sck,
+            'subprotocols': pytest.saltyrtc.subprotocols,
+        })
+        ccsn += 1
+
+        # Expect protocol error
+        yield from server.wait_connections_closed()
+        assert not client.ws_client.open
+        assert client.ws_client.close_code == CloseCode.protocol_error
+
     @pytest.mark.asyncio
     def test_client_factory_handshake(
             self, server, client_factory, initiator_key, responder_key
@@ -633,6 +693,37 @@ def test_invalid_destination_after_handshake(
         assert not responder.ws_client.open
         assert responder.ws_client.close_code == CloseCode.protocol_error
 
+    @pytest.mark.asyncio
+    def test_unencrypted_packet_after_initiator_handshake(
+            self, pack_nonce, server, client_factory
+    ):
+        """
+        Check that the server closes with Protocol Error when an
+        unencrypted packet is being sent by an initiator.
+        """
+        # Initiator handshake
+        initiator, i = yield from client_factory(initiator_handshake=True)
+        assert len(i['responders']) == 0
+
+        # Drop non-existing responder (encrypted)
+        yield from initiator.send(pack_nonce(i['cck'], 0x01, 0x00, i['ccsn']), {
+            'type': 'drop-responder',
+            'id': 0x02,
+        })
+        i['ccsn'] += 1
+
+        # Drop non-existing responder (unencrypted)
+        yield from initiator.send(pack_nonce(i['cck'], 0x01, 0x00, i['ccsn']), {
+            'type': 'drop-responder',
+            'id': 0x02,
+        }, box=None)
+        i['ccsn'] += 1
+
+        # Expect protocol error
+        yield from server.wait_connections_closed()
+        assert not initiator.ws_client.open
+        assert initiator.ws_client.close_code == CloseCode.protocol_error
+
     @pytest.mark.asyncio
     def test_new_initiator(self, server, client_factory):
         """