diff --git a/src/pgmq/queue.py b/src/pgmq/queue.py
index 8883567..2ed6d5a 100644
--- a/src/pgmq/queue.py
+++ b/src/pgmq/queue.py
@@ -37,6 +37,7 @@ def __post_init__(self) -> None:
         user={self.username}
         password={self.password}
         """
+        self.kwargs.setdefault("max_size", self.pool_size)
         self.pool = ConnectionPool(conninfo, open=True, **self.kwargs)
         self._initialize_logging()
         if self.init_extension: