diff --git a/nonebot/plugins/single_session.py b/nonebot/plugins/single_session.py
index d0e5b4a6..11b5b6cc 100644
--- a/nonebot/plugins/single_session.py
+++ b/nonebot/plugins/single_session.py
@@ -21,7 +21,7 @@ async def matcher_mutex(event: Event) -> Generator[bool, None, None]:
         else:
             _running_matcher[session_id] = current_event_id
         yield result
-        if result:
+        if not result:
             del _running_matcher[session_id]
 
 
diff --git a/tests/test_single_session.py b/tests/test_single_session.py
index f0a696d5..1a2bc67f 100644
--- a/tests/test_single_session.py
+++ b/tests/test_single_session.py
@@ -7,22 +7,30 @@ from utils import make_fake_event
 
 @pytest.mark.asyncio
 async def test_matcher_mutex():
-    from nonebot.plugins.single_session import matcher_mutex
+    from nonebot.plugins.single_session import matcher_mutex, _running_matcher
 
     am = asynccontextmanager(matcher_mutex)
     event = make_fake_event()()
     event_1 = make_fake_event()()
     event_2 = make_fake_event(_session_id="test1")()
+    event_3 = make_fake_event(_session_id=None)()
 
     async with am(event) as ctx:
         assert ctx == False
+    assert not _running_matcher
 
     async with am(event) as ctx:
         async with am(event_1) as ctx_1:
             assert ctx == False
             assert ctx_1 == True
+    assert not _running_matcher
 
     async with am(event) as ctx:
         async with am(event_2) as ctx_2:
             assert ctx == False
             assert ctx_2 == False
+    assert not _running_matcher
+
+    async with am(event_3) as ctx_3:
+        assert ctx_3 == False
+    assert not _running_matcher
diff --git a/tests/utils.py b/tests/utils.py
index 711c7c05..e82ad7d9 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -50,7 +50,7 @@ def make_fake_event(
     _name: str = "test",
     _description: str = "test",
     _user_id: str = "test",
-    _session_id: str = "test",
+    _session_id: Optional[str] = "test",
     _message: Optional["Message"] = None,
     _to_me: bool = True,
     **fields,
@@ -73,7 +73,9 @@ def make_fake_event(
             return _user_id
 
         def get_session_id(self) -> str:
-            return _session_id
+            if _session_id is not None:
+                return _session_id
+            raise NotImplementedError
 
         def get_message(self) -> "Message":
             if _message is not None: