diff --git a/httpx/_client.py b/httpx/_client.py
index 4661b221c5..2fc62c935a 100644
--- a/httpx/_client.py
+++ b/httpx/_client.py
@@ -859,7 +859,7 @@ def _send_single_request(self, request: Request, timeout: Timeout) -> Response:
             )
 
         def on_close(response: Response) -> None:
-            response.elapsed = datetime.timedelta(timer.sync_elapsed())
+            response.elapsed = datetime.timedelta(seconds=timer.sync_elapsed())
             if hasattr(stream, "close"):
                 stream.close()
 
@@ -1504,7 +1504,7 @@ async def _send_single_request(
             )
 
         async def on_close(response: Response) -> None:
-            response.elapsed = datetime.timedelta(await timer.async_elapsed())
+            response.elapsed = datetime.timedelta(seconds=await timer.async_elapsed())
             if hasattr(stream, "close"):
                 await stream.aclose()