diff --git a/httpcore/_async/connection_pool.py b/httpcore/_async/connection_pool.py
index 089271344..a487990a8 100644
--- a/httpcore/_async/connection_pool.py
+++ b/httpcore/_async/connection_pool.py
@@ -237,6 +237,7 @@ async def handle_async_request(
                 # behind catching 'BaseException' rather than 'Exception' here.
                 logger.trace("remove from pool connection=%r", connection)
                 await self._remove_from_pool(connection)
+                await connection.aclose()
                 raise
 
         status_code, headers, stream, extensions = response
diff --git a/httpcore/_sync/connection_pool.py b/httpcore/_sync/connection_pool.py
index a60437b64..12b2d6565 100644
--- a/httpcore/_sync/connection_pool.py
+++ b/httpcore/_sync/connection_pool.py
@@ -237,6 +237,7 @@ def handle_request(
                 # behind catching 'BaseException' rather than 'Exception' here.
                 logger.trace("remove from pool connection=%r", connection)
                 self._remove_from_pool(connection)
+                connection.close()
                 raise
 
         status_code, headers, stream, extensions = response