diff --git a/src/websockets/extensions/base.py b/src/websockets/extensions/base.py
index 42dd6c5f..2fdc59f0 100644
--- a/src/websockets/extensions/base.py
+++ b/src/websockets/extensions/base.py
@@ -58,7 +58,7 @@ class ClientExtensionFactory:
     name: ExtensionName
     """Extension identifier."""
 
-    def get_request_params(self) -> list[ExtensionParameter]:
+    def get_request_params(self) -> Sequence[ExtensionParameter]:
         """
         Build parameters to send to the server for this extension.
 
diff --git a/src/websockets/extensions/permessage_deflate.py b/src/websockets/extensions/permessage_deflate.py
index 8e74cb28..7e9e7a5d 100644
--- a/src/websockets/extensions/permessage_deflate.py
+++ b/src/websockets/extensions/permessage_deflate.py
@@ -351,7 +351,7 @@ def __init__(
         self.client_max_window_bits = client_max_window_bits
         self.compress_settings = compress_settings
 
-    def get_request_params(self) -> list[ExtensionParameter]:
+    def get_request_params(self) -> Sequence[ExtensionParameter]:
         """
         Build request parameters.
 
diff --git a/src/websockets/headers.py b/src/websockets/headers.py
index c42abd97..e05ff5b4 100644
--- a/src/websockets/headers.py
+++ b/src/websockets/headers.py
@@ -390,7 +390,7 @@ def parse_extension(header: str) -> list[ExtensionHeader]:
 
 
 def build_extension_item(
-    name: ExtensionName, parameters: list[ExtensionParameter]
+    name: ExtensionName, parameters: Sequence[ExtensionParameter]
 ) -> str:
     """
     Build an extension definition.
diff --git a/src/websockets/typing.py b/src/websockets/typing.py
index f10481b8..ab7ddd33 100644
--- a/src/websockets/typing.py
+++ b/src/websockets/typing.py
@@ -2,7 +2,7 @@
 
 import http
 import logging
-from typing import TYPE_CHECKING, Any, NewType, Optional, Union
+from typing import TYPE_CHECKING, Any, NewType, Optional, Sequence, Union
 
 
 __all__ = [
@@ -62,7 +62,7 @@
 
 # Private types
 
-ExtensionHeader = tuple[ExtensionName, list[ExtensionParameter]]
+ExtensionHeader = tuple[ExtensionName, Sequence[ExtensionParameter]]
 """Extension in a ``Sec-WebSocket-Extensions`` header."""