diff --git a/telegram/ext/conversationhandler.py b/telegram/ext/conversationhandler.py
index beb299597..ec91b11d4 100644
--- a/telegram/ext/conversationhandler.py
+++ b/telegram/ext/conversationhandler.py
@@ -592,6 +592,11 @@ class ConversationHandler(Handler[Update]):
                     )
 
         elif new_state is not None:
+            if new_state not in self.states:
+                warnings.warn(
+                    f"Handler returned state {new_state} which is unknown to the "
+                    f"ConversationHandler{' ' + self.name if self.name is not None else ''}."
+                )
             with self._conversations_lock:
                 self.conversations[key] = new_state
                 if self.persistent and self.persistence and self.name:
diff --git a/telegram/ext/dispatcher.py b/telegram/ext/dispatcher.py
index 0baacbaed..7c77e88b5 100644
--- a/telegram/ext/dispatcher.py
+++ b/telegram/ext/dispatcher.py
@@ -162,6 +162,11 @@ class Dispatcher:
                 stacklevel=3,
             )
 
+        if self.workers < 1:
+            warnings.warn(
+                'Asynchronous callbacks can not be processed without at least one worker thread.'
+            )
+
         self.user_data: DefaultDict[int, Dict[object, object]] = defaultdict(dict)
         self.chat_data: DefaultDict[int, Dict[object, object]] = defaultdict(dict)
         self.bot_data = {}
diff --git a/tests/test_conversationhandler.py b/tests/test_conversationhandler.py
index 28a6dd130..f5950e6fa 100644
--- a/tests/test_conversationhandler.py
+++ b/tests/test_conversationhandler.py
@@ -433,6 +433,37 @@ class TestConversationHandler:
         dp.process_update(Update(update_id=0, message=message))
         assert self.current_state[user1.id] == self.THIRSTY
 
+    def test_unknown_state_warning(self, dp, bot, user1, recwarn):
+        handler = ConversationHandler(
+            entry_points=[CommandHandler("start", lambda u, c: 1)],
+            states={
+                1: [TypeHandler(Update, lambda u, c: 69)],
+                2: [TypeHandler(Update, lambda u, c: -1)],
+            },
+            fallbacks=self.fallbacks,
+            name="xyz",
+        )
+        dp.add_handler(handler)
+        message = Message(
+            0,
+            None,
+            self.group,
+            from_user=user1,
+            text='/start',
+            entities=[
+                MessageEntity(type=MessageEntity.BOT_COMMAND, offset=0, length=len('/start'))
+            ],
+            bot=bot,
+        )
+        dp.process_update(Update(update_id=0, message=message))
+        sleep(0.5)
+        dp.process_update(Update(update_id=1, message=message))
+        sleep(0.5)
+        assert len(recwarn) == 1
+        assert str(recwarn[0].message) == (
+            "Handler returned state 69 which is unknown to the ConversationHandler xyz."
+        )
+
     def test_conversation_handler_per_chat(self, dp, bot, user1, user2):
         handler = ConversationHandler(
             entry_points=self.entry_points,
diff --git a/tests/test_dispatcher.py b/tests/test_dispatcher.py
index 83550e689..375174b12 100644
--- a/tests/test_dispatcher.py
+++ b/tests/test_dispatcher.py
@@ -97,6 +97,14 @@ class TestDispatcher:
         ):
             self.received = context.error.message
 
+    def test_less_than_one_worker_warning(self, dp, recwarn):
+        Dispatcher(dp.bot, dp.update_queue, job_queue=dp.job_queue, workers=0, use_context=True)
+        assert len(recwarn) == 1
+        assert (
+            str(recwarn[0].message)
+            == 'Asynchronous callbacks can not be processed without at least one worker thread.'
+        )
+
     def test_one_context_per_update(self, cdp):
         def one(update, context):
             if update.message.text == 'test':