diff --git a/dist/mcp/index.js b/dist/mcp/index.js
index 1edcf0c8..e65cd346 100644
--- a/dist/mcp/index.js
+++ b/dist/mcp/index.js
@@ -32,9 +32,9 @@ const KEEPALIVE_FRAME = ": keepalive\n\n";
 * Start an SSE keepalive on `writer`. Returns a `clearInterval` handle
 * that the stream cleanup must invoke when the stream closes.
 */
-function startKeepalive(writer, encoder) {
+function startKeepalive(writeFrame, encoder) {
 	const handle = setInterval(() => {
-		writer.write(encoder.encode(KEEPALIVE_FRAME)).catch(() => clearInterval(handle));
+		writeFrame(encoder.encode(KEEPALIVE_FRAME));
 	}, KEEPALIVE_INTERVAL_MS);
 	return handle;
 }
@@ -180,10 +180,15 @@ const createStreamingHttpHandler = (basePath, namespace, options = {}) => {
 					});
 					return new Response(body, { status: 404 });
 				}
-				const { readable, writable } = new TransformStream();
-				const writer = writable.getWriter();
-				const encoder = new TextEncoder();
-				const existingHeaders = {};
+					const { readable, writable } = new TransformStream();
+					const writer = writable.getWriter();
+					const encoder = new TextEncoder();
+					const MAX_PENDING_SSE_BYTES = 8 * 1024 * 1024;
+					let __pendingBytes = 0;
+					let __writeChain = Promise.resolve();
+					let __sseClosed = false;
+					let keepAlive;
+					const existingHeaders = {};
 				request.headers.forEach((value, key) => {
 					existingHeaders[key] = value;
 				});
@@ -206,45 +211,68 @@ const createStreamingHttpHandler = (basePath, namespace, options = {}) => {
 						jsonrpc: "2.0"
 					});
 					return new Response(body, { status: 500 });
-				}
-				ws.accept();
-				if (messages.every((msg) => isJSONRPCNotification(msg) || isJSONRPCResultResponse(msg))) {
-					ws.close();
-					return new Response(null, {
+					}
+					ws.accept();
+					const __forwardSse = (frame) => {
+						if (__sseClosed) return __writeChain;
+						if (__pendingBytes + frame.byteLength > MAX_PENDING_SSE_BYTES) {
+							__sseClosed = true;
+							try {
+								clearInterval(keepAlive);
+							} catch {}
+							try {
+								ws.close(1013, "SSE client not draining");
+							} catch {}
+							writer.abort(new Error("SSE client not draining")).catch(() => {});
+							return Promise.resolve();
+						}
+						__pendingBytes += frame.byteLength;
+						__writeChain = __writeChain.then(() => writer.write(frame)).catch(() => {}).finally(() => {
+							__pendingBytes -= frame.byteLength;
+						});
+						return __writeChain;
+					};
+					keepAlive = startKeepalive(__forwardSse, encoder);
+					if (messages.every((msg) => isJSONRPCNotification(msg) || isJSONRPCResultResponse(msg))) {
+						clearInterval(keepAlive);
+						ws.close();
+						return new Response(null, {
 						headers: corsHeaders(request, options.corsOptions),
 						status: 202
-					});
-				}
-				const keepAlive = startKeepalive(writer, encoder);
-				ws.addEventListener("message", (event) => {
+						});
+					}
+					ws.addEventListener("message", (event) => {
 					async function onMessage(event) {
 						try {
-							const data = typeof event.data === "string" ? event.data : new TextDecoder().decode(event.data);
-							const message = JSON.parse(data);
-							if (message.type !== "cf_mcp_agent_event") return;
-							await writer.write(encoder.encode(message.event));
-							if (message.close) {
-								clearInterval(keepAlive);
-								ws?.close();
-								await writer.close().catch(() => {});
-							}
+								const data = typeof event.data === "string" ? event.data : new TextDecoder().decode(event.data);
+								const message = JSON.parse(data);
+								if (message.type !== "cf_mcp_agent_event") return;
+								const writePromise = __forwardSse(encoder.encode(message.event));
+								if (message.close) {
+									clearInterval(keepAlive);
+									ws?.close();
+									await writePromise;
+									await writer.close().catch(() => {});
+								}
 						} catch (error) {
 							console.error("Error forwarding message to SSE:", error);
 						}
 					}
 					onMessage(event).catch(console.error);
 				});
-				ws.addEventListener("error", (error) => {
-					async function onError(_error) {
-						clearInterval(keepAlive);
-						await writer.close().catch(() => {});
+					ws.addEventListener("error", (error) => {
+						async function onError(_error) {
+							__sseClosed = true;
+							clearInterval(keepAlive);
+							await writer.close().catch(() => {});
 					}
 					onError(error).catch(console.error);
 				});
-				ws.addEventListener("close", () => {
-					async function onClose() {
-						clearInterval(keepAlive);
-						await writer.close().catch(() => {});
+					ws.addEventListener("close", () => {
+						async function onClose() {
+							__sseClosed = true;
+							clearInterval(keepAlive);
+							await writer.close().catch(() => {});
 					}
 					onClose().catch(console.error);
 				});
@@ -279,10 +307,15 @@ const createStreamingHttpHandler = (basePath, namespace, options = {}) => {
 					id: null,
 					jsonrpc: "2.0"
 				}), { status: 400 });
-				const { readable, writable } = new TransformStream();
-				const writer = writable.getWriter();
-				const encoder = new TextEncoder();
-				const agent = await getAgentByName(namespace, `streamable-http:${sessionId}`, {
+					const { readable, writable } = new TransformStream();
+					const writer = writable.getWriter();
+					const encoder = new TextEncoder();
+					const MAX_PENDING_SSE_BYTES = 8 * 1024 * 1024;
+					let __pendingBytes = 0;
+					let __writeChain = Promise.resolve();
+					let __sseClosed = false;
+					let keepAlive;
+					const agent = await getAgentByName(namespace, `streamable-http:${sessionId}`, {
 					props: ctx.props,
 					jurisdiction: options.jurisdiction
 				});
@@ -306,27 +339,51 @@ const createStreamingHttpHandler = (basePath, namespace, options = {}) => {
 				if (!ws) {
 					await writer.close();
 					return new Response("Failed to establish WS to DO", { status: 500 });
-				}
-				ws.accept();
-				ws.addEventListener("message", (event) => {
+					}
+					ws.accept();
+					const __forwardSse = (frame) => {
+						if (__sseClosed) return __writeChain;
+						if (__pendingBytes + frame.byteLength > MAX_PENDING_SSE_BYTES) {
+							__sseClosed = true;
+							try {
+								clearInterval(keepAlive);
+							} catch {}
+							try {
+								ws.close(1013, "SSE client not draining");
+							} catch {}
+							writer.abort(new Error("SSE client not draining")).catch(() => {});
+							return Promise.resolve();
+						}
+						__pendingBytes += frame.byteLength;
+						__writeChain = __writeChain.then(() => writer.write(frame)).catch(() => {}).finally(() => {
+							__pendingBytes -= frame.byteLength;
+						});
+						return __writeChain;
+					};
+					keepAlive = startKeepalive(__forwardSse, encoder);
+					ws.addEventListener("message", (event) => {
 					try {
 						async function onMessage(ev) {
-							const data = typeof ev.data === "string" ? ev.data : new TextDecoder().decode(ev.data);
-							const message = JSON.parse(data);
-							if (message.type !== "cf_mcp_agent_event") return;
-							await writer.write(encoder.encode(message.event));
-						}
+								const data = typeof ev.data === "string" ? ev.data : new TextDecoder().decode(ev.data);
+								const message = JSON.parse(data);
+								if (message.type !== "cf_mcp_agent_event") return;
+								__forwardSse(encoder.encode(message.event));
+							}
 						onMessage(event).catch(console.error);
 					} catch (e) {
 						console.error("Error forwarding message to SSE:", e);
 					}
-				});
-				ws.addEventListener("error", () => {
-					writer.close().catch(() => {});
-				});
-				ws.addEventListener("close", () => {
-					writer.close().catch(() => {});
-				});
+					});
+					ws.addEventListener("error", () => {
+						__sseClosed = true;
+						clearInterval(keepAlive);
+						writer.close().catch(() => {});
+					});
+					ws.addEventListener("close", () => {
+						__sseClosed = true;
+						clearInterval(keepAlive);
+						writer.close().catch(() => {});
+					});
 				return new Response(readable, {
 					headers: {
 						"Cache-Control": "no-cache",
@@ -389,10 +446,15 @@ const createLegacySseHandler = (basePath, namespace, options = {}) => {
 		const url = new URL(request.url);
 		if (request.method === "GET" && basePattern.test(url)) {
 			const sessionId = url.searchParams.get("sessionId") || namespace.newUniqueId().toString();
-			const { readable, writable } = new TransformStream();
-			const writer = writable.getWriter();
-			const encoder = new TextEncoder();
-			const endpointUrl = new URL(request.url);
+				const { readable, writable } = new TransformStream();
+				const writer = writable.getWriter();
+				const encoder = new TextEncoder();
+				const MAX_PENDING_SSE_BYTES = 8 * 1024 * 1024;
+				let __pendingBytes = 0;
+				let __writeChain = Promise.resolve();
+				let __sseClosed = false;
+				let keepAlive;
+				const endpointUrl = new URL(request.url);
 			endpointUrl.pathname = encodeURI(`${basePath}/message`);
 			endpointUrl.searchParams.set("sessionId", sessionId);
 			const endpointMessage = `event: endpoint\ndata: ${endpointUrl.pathname + endpointUrl.search + endpointUrl.hash}\n\n`;
@@ -414,35 +476,59 @@ const createLegacySseHandler = (basePath, namespace, options = {}) => {
 				console.error("Failed to establish WebSocket connection");
 				await writer.close();
 				return new Response("Failed to establish WebSocket connection", { status: 500 });
-			}
-			ws.accept();
-			ws.addEventListener("message", (event) => {
+				}
+				ws.accept();
+				const __forwardSse = (frame) => {
+					if (__sseClosed) return __writeChain;
+					if (__pendingBytes + frame.byteLength > MAX_PENDING_SSE_BYTES) {
+						__sseClosed = true;
+						try {
+							clearInterval(keepAlive);
+						} catch {}
+						try {
+							ws.close(1013, "SSE client not draining");
+						} catch {}
+						writer.abort(new Error("SSE client not draining")).catch(() => {});
+						return Promise.resolve();
+					}
+					__pendingBytes += frame.byteLength;
+					__writeChain = __writeChain.then(() => writer.write(frame)).catch(() => {}).finally(() => {
+						__pendingBytes -= frame.byteLength;
+					});
+					return __writeChain;
+				};
+				keepAlive = startKeepalive(__forwardSse, encoder);
+				ws.addEventListener("message", (event) => {
 				async function onMessage(event) {
 					try {
 						const message = JSON.parse(event.data);
-						const result = JSONRPCMessageSchema.safeParse(message);
-						if (!result.success) return;
-						const messageText = `event: message\ndata: ${JSON.stringify(result.data)}\n\n`;
-						await writer.write(encoder.encode(messageText));
-					} catch (error) {
+							const result = JSONRPCMessageSchema.safeParse(message);
+							if (!result.success) return;
+							const messageText = `event: message\ndata: ${JSON.stringify(result.data)}\n\n`;
+							__forwardSse(encoder.encode(messageText));
+						} catch (error) {
 						console.error("Error forwarding message to SSE:", error);
 					}
 				}
 				onMessage(event).catch(console.error);
 			});
-			ws.addEventListener("error", (error) => {
-				async function onError(_error) {
-					try {
-						await writer.close();
-					} catch (_e) {}
+				ws.addEventListener("error", (error) => {
+					async function onError(_error) {
+						try {
+							__sseClosed = true;
+							clearInterval(keepAlive);
+							await writer.close();
+						} catch (_e) {}
 				}
 				onError(error).catch(console.error);
 			});
-			ws.addEventListener("close", () => {
-				async function onClose() {
-					try {
-						await writer.close();
-					} catch (error) {
+				ws.addEventListener("close", () => {
+					async function onClose() {
+						try {
+							__sseClosed = true;
+							clearInterval(keepAlive);
+							await writer.close();
+						} catch (error) {
 						console.error("Error closing SSE connection:", error);
 					}
 				}
@@ -1700,4 +1786,4 @@ McpAgent.STREAM_REQS_KEY_PREFIX = "__mcp_stream_reqs__:";
 //#endregion
 export { DurableObjectEventStore, ElicitRequestSchema, MCP_SERVER_ID_MAX_LENGTH, McpAgent, RPCClientTransport, RPCServerTransport, RPC_DO_PREFIX, SSEEdgeClientTransport, StreamableHTTPEdgeClientTransport, WorkerTransport, createMcpHandler, experimental_createMcpHandler, getMcpAuthContext, normalizeServerId };
 
-//# sourceMappingURL=index.js.map
\ No newline at end of file
+//# sourceMappingURL=index.js.map