diff --git a/.github/workflows/tests.yaml b/.github/workflows/tests.yaml
index a952126..625547a 100644
--- a/.github/workflows/tests.yaml
+++ b/.github/workflows/tests.yaml
@@ -32,6 +32,7 @@ jobs:
       - name: Install Poetry
         uses: snok/install-poetry@v1
         with:
+          version: 1.8.5
           virtualenvs-create: true
           virtualenvs-in-project: true
       - name: Load cached venv
diff --git a/aioimaplib/aioimaplib.py b/aioimaplib/aioimaplib.py
index 1130ef5..216060e 100644
--- a/aioimaplib/aioimaplib.py
+++ b/aioimaplib/aioimaplib.py
@@ -525,7 +525,7 @@ def has_pending_idle_command(self) -> bool:
     def idle_done(self) -> None:
         self.send('DONE')
 
-    async def search(self, *criteria, charset: Optional[str] = 'utf-8', by_uid: bool = False) -> Response:
+    async def search(self, *criteria, charset: Optional[str] = None, by_uid: bool = False) -> Response:
         args = ('CHARSET', charset) + criteria if charset is not None else criteria
         prefix = 'UID' if by_uid else ''
 
@@ -738,10 +738,10 @@ async def logout(self) -> Response:
     async def select(self, mailbox: str = 'INBOX') -> Response:
         return await asyncio.wait_for(self.protocol.select(mailbox), self.timeout)
 
-    async def search(self, *criteria: str, charset: Optional[str] = 'utf-8') -> Response:
+    async def search(self, *criteria: str, charset: Optional[str] = None) -> Response:
         return await asyncio.wait_for(self.protocol.search(*criteria, charset=charset), self.timeout)
 
-    async def uid_search(self, *criteria: str, charset: Optional[str] = 'utf-8') -> Response:
+    async def uid_search(self, *criteria: str, charset: Optional[str] = None) -> Response:
         return await asyncio.wait_for(self.protocol.search(*criteria, by_uid=True, charset=charset), self.timeout)
 
     async def uid(self, command: str, *criteria: str) -> Response:
diff --git a/tests/test_aioimaplib.py b/tests/test_aioimaplib.py
index a3adc99..d6adeab 100644
--- a/tests/test_aioimaplib.py
+++ b/tests/test_aioimaplib.py
@@ -339,6 +339,33 @@ async def test_search_two_messages(with_server):
     assert b'1 2' == data[0]
 
 
+@pytest.mark.asyncio()
+async def test_search_default_charset_is_none(with_server):
+    """Default charset should be None to avoid sending CHARSET which some servers reject."""
+    with_server.receive(Mail.create(['user']))
+    imap_client = await login_user_async('user', 'pass', select=True)
+
+    # Default charset=None should work (no CHARSET sent)
+    result, data = await imap_client.search('ALL')
+    assert 'OK' == result
+    assert b'1' == data[0]
+
+    # Explicit charset='utf-8' should still work
+    result, data = await imap_client.search('ALL', charset='utf-8')
+    assert 'OK' == result
+    assert b'1' == data[0]
+
+    # uid_search default charset=None should work
+    result, data = await imap_client.uid_search('ALL')
+    assert 'OK' == result
+    assert b'1' == data[0]
+
+    # uid_search explicit charset='utf-8' should still work
+    result, data = await imap_client.uid_search('ALL', charset='utf-8')
+    assert 'OK' == result
+    assert b'1' == data[0]
+
+
 @pytest.mark.asyncio()
 async def test_search_messages(with_server):
     """Increase compatibility with https://docs.python.org/3/library/imaplib.html#imap4-example."""