diff --git a/httpcore/_async/connection_pool.py b/httpcore/_async/connection_pool.py
index 214dfc4b..da43b8dc 100644
--- a/httpcore/_async/connection_pool.py
+++ b/httpcore/_async/connection_pool.py
@@ -251,7 +251,13 @@ def _assign_requests_to_connections(self) -> List[AsyncConnectionInterface]:
                 closing_connections.append(connection)
             elif (
                 connection.is_idle()
-                and len([connection.is_idle() for connection in self._connections])
+                and len(
+                    [
+                        connection
+                        for connection in self._connections
+                        if connection.is_idle()
+                    ]
+                )
                 > self._max_keepalive_connections
             ):
                 # log: "closing idle connection"
diff --git a/httpcore/_sync/connection_pool.py b/httpcore/_sync/connection_pool.py
index 01bec59e..13087c01 100644
--- a/httpcore/_sync/connection_pool.py
+++ b/httpcore/_sync/connection_pool.py
@@ -251,7 +251,13 @@ def _assign_requests_to_connections(self) -> List[ConnectionInterface]:
                 closing_connections.append(connection)
             elif (
                 connection.is_idle()
-                and len([connection.is_idle() for connection in self._connections])
+                and len(
+                    [
+                        connection
+                        for connection in self._connections
+                        if connection.is_idle()
+                    ]
+                )
                 > self._max_keepalive_connections
             ):
                 # log: "closing idle connection"