diff --git a/homeassistant/components/websocket_api/messages.py b/homeassistant/components/websocket_api/messages.py
index 52e97b60ccf..f68beff5924 100644
--- a/homeassistant/components/websocket_api/messages.py
+++ b/homeassistant/components/websocket_api/messages.py
@@ -12,6 +12,7 @@ from homeassistant.util.json import (
     find_paths_unserializable_data,
     format_unserializable_data,
 )
+from homeassistant.util.yaml.loader import JSON_TYPE
 
 from . import const
 
@@ -27,6 +28,9 @@ MINIMAL_MESSAGE_SCHEMA = vol.Schema(
 # Base schema to extend by message handlers
 BASE_COMMAND_MESSAGE_SCHEMA = vol.Schema({vol.Required("id"): cv.positive_int})
 
+IDEN_TEMPLATE = "__IDEN__"
+IDEN_JSON_TEMPLATE = '"__IDEN__"'
+
 
 def result_message(iden: int, result: Any = None) -> Dict:
     """Return a success result message."""
@@ -43,12 +47,11 @@ def error_message(iden: int, code: str, message: str) -> Dict:
     }
 
 
-def event_message(iden: int, event: Any) -> Dict:
+def event_message(iden: JSON_TYPE, event: Any) -> Dict:
     """Return an event message."""
     return {"id": iden, "type": "event", "event": event}
 
 
-@lru_cache(maxsize=128)
 def cached_event_message(iden: int, event: Event) -> str:
     """Return an event message.
 
@@ -58,7 +61,17 @@ def cached_event_message(iden: int, event: Event) -> str:
     all getting many of the same events (mostly state changed)
     we can avoid serializing the same data for each connection.
     """
-    return message_to_json(event_message(iden, event))
+    return _cached_event_message(event).replace(IDEN_JSON_TEMPLATE, str(iden), 1)
+
+
+@lru_cache(maxsize=128)
+def _cached_event_message(event: Event) -> str:
+    """Cache and serialize the event to json.
+
+    The IDEN_TEMPLATE is used which will be replaced
+    with the actual iden in cached_event_message
+    """
+    return message_to_json(event_message(IDEN_TEMPLATE, event))
 
 
 def message_to_json(message: Any) -> str:
diff --git a/tests/components/websocket_api/test_messages.py b/tests/components/websocket_api/test_messages.py
index 832b72c5c1c..3ec156e6949 100644
--- a/tests/components/websocket_api/test_messages.py
+++ b/tests/components/websocket_api/test_messages.py
@@ -1,6 +1,7 @@
 """Test Websocket API messages module."""
 
 from homeassistant.components.websocket_api.messages import (
+    _cached_event_message as lru_event_cache,
     cached_event_message,
     message_to_json,
 )
@@ -24,6 +25,7 @@ async def test_cached_event_message(hass):
     await hass.async_block_till_done()
 
     assert len(events) == 2
+    lru_event_cache.cache_clear()
 
     msg0 = cached_event_message(2, events[0])
     assert msg0 == cached_event_message(2, events[0])
@@ -33,18 +35,49 @@ async def test_cached_event_message(hass):
 
     assert msg0 != msg1
 
-    cache_info = cached_event_message.cache_info()
+    cache_info = lru_event_cache.cache_info()
     assert cache_info.hits == 2
     assert cache_info.misses == 2
     assert cache_info.currsize == 2
 
     cached_event_message(2, events[1])
-    cache_info = cached_event_message.cache_info()
+    cache_info = lru_event_cache.cache_info()
     assert cache_info.hits == 3
     assert cache_info.misses == 2
     assert cache_info.currsize == 2
 
 
+async def test_cached_event_message_with_different_idens(hass):
+    """Test that we cache event messages when the subscrition idens differ."""
+
+    events = []
+
+    @callback
+    def _event_listener(event):
+        events.append(event)
+
+    hass.bus.async_listen(EVENT_STATE_CHANGED, _event_listener)
+
+    hass.states.async_set("light.window", "on")
+    await hass.async_block_till_done()
+
+    assert len(events) == 1
+
+    lru_event_cache.cache_clear()
+
+    msg0 = cached_event_message(2, events[0])
+    msg1 = cached_event_message(3, events[0])
+    msg2 = cached_event_message(4, events[0])
+
+    assert msg0 != msg1
+    assert msg0 != msg2
+
+    cache_info = lru_event_cache.cache_info()
+    assert cache_info.hits == 2
+    assert cache_info.misses == 1
+    assert cache_info.currsize == 1
+
+
 async def test_message_to_json(caplog):
     """Test we can serialize websocket messages."""