diff --git a/src/mcp/server/streamable_http.py b/src/mcp/server/streamable_http.py
index f2f4407ce..bfe3abcd7 100644
--- a/src/mcp/server/streamable_http.py
+++ b/src/mcp/server/streamable_http.py
@@ -771,6 +771,11 @@ async def terminate(self) -> None:
         self._terminated = True
         logger.info(f"Terminating session: {self.mcp_session_id}")
 
+        # Close all SSE stream writers to allow EventSourceResponse to complete gracefully
+        for writer in list(self._sse_stream_writers.values()):
+            writer.close()
+        self._sse_stream_writers.clear()
+
         # We need a copy of the keys to avoid modification during iteration
         request_stream_keys = list(self._request_streams.keys())
 
diff --git a/src/mcp/server/streamable_http_manager.py b/src/mcp/server/streamable_http_manager.py
index 81350a8f2..b9a27a41f 100644
--- a/src/mcp/server/streamable_http_manager.py
+++ b/src/mcp/server/streamable_http_manager.py
@@ -133,6 +133,12 @@ async def lifespan(app: Starlette) -> AsyncIterator[None]:
                 yield  # Let the application run
             finally:
                 logger.info("StreamableHTTP session manager shutting down")
+                # Gracefully terminate all active sessions before cancelling tasks
+                for transport in list(self._server_instances.values()):
+                    try:
+                        await transport.terminate()
+                    except Exception:
+                        logger.debug("Error terminating transport during shutdown", exc_info=True)
                 # Cancel task group to stop all spawned tasks
                 tg.cancel_scope.cancel()
                 self._task_group = None