diff --git a/amqtt/client.py b/amqtt/client.py
index 8da9aba..1828f02 100644
--- a/amqtt/client.py
+++ b/amqtt/client.py
@@ -470,6 +470,7 @@ class MQTTClient:
             reader: StreamReaderAdapter | WebSocketsReader | None = None
             writer: StreamWriterAdapter | WebSocketsWriter | None = None
             self._connected_state.clear()
+
             # Open connection
             if scheme in ("mqtt", "mqtts"):
                 conn_reader, conn_writer = await asyncio.open_connection(
@@ -489,11 +490,11 @@ class MQTTClient:
                 )
                 reader = WebSocketsReader(websocket)
                 writer = WebSocketsWriter(websocket)
-
-            if reader is None or writer is None:
-                self.session.transitions.disconnect()
-                self.logger.warning("reader or writer not initialized")
-                msg = "reader or writer not initialized"
+            elif not self.session.broker_uri:
+                msg = "missing broker uri"
+                raise ClientError(msg)
+            else:
+                msg = f"incorrect scheme defined in uri: '{scheme!r}'"
                 raise ClientError(msg)
 
             # Start MQTT protocol
diff --git a/tests/test_client.py b/tests/test_client.py
index 7d56274..8962d21 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -4,7 +4,7 @@ import logging
 import pytest
 
 from amqtt.client import MQTTClient
-from amqtt.errors import ConnectError
+from amqtt.errors import ClientError, ConnectError
 from amqtt.mqtt.constants import QOS_0, QOS_1, QOS_2
 
 formatter = "[%(asctime)s] %(name)s {%(filename)s:%(lineno)d} %(levelname)s - %(message)s"
@@ -301,4 +301,14 @@ async def test_client_publish_will_with_retain(broker_fixture, client_config):
 async def test_connect_broken_uri():
     config = {"auto_reconnect": False}
     client = MQTTClient(config=config)
-    await client.connect('"mqtt://someplace')
+    with pytest.raises(ClientError):
+        await client.connect('"mqtt://someplace')
+
+
+@pytest.mark.asyncio
+async def test_connect_incorrect_scheme():
+    config = {"auto_reconnect": False}
+    client = MQTTClient(config=config)
+    with pytest.raises(ClientError):
+        await client.connect('"mq://someplace')
+