diff --git a/open-sse/utils/proxyDispatcher.ts b/open-sse/utils/proxyDispatcher.ts
index 6166df9604..879ec80aca 100644
--- a/open-sse/utils/proxyDispatcher.ts
+++ b/open-sse/utils/proxyDispatcher.ts
@@ -20,6 +20,23 @@ export function clearDispatcherCache() {
   cache.clear();
 }
 
+/**
+ * Extract the port from a proxy URL string before URL parsing.
+ * `new URL("http://host:80")` strips port 80 since it's the HTTP default,
+ * but proxy servers commonly listen on port 80/443, so we need to preserve it.
+ */
+function extractExplicitPort(urlStr) {
+  try {
+    // Match port in the host portion: "scheme://[user:pass@]host:PORT[/...]"
+    const match = urlStr.match(/:\/\/(?:[^@]*@)?[^:/\s]+:(\d+)/);
+    if (match) {
+      const port = Number(match[1]);
+      if (Number.isInteger(port) && port >= 1 && port <= 65535) return String(port);
+    }
+  } catch {}
+  return null;
+}
+
 function defaultPortForProtocol(protocol) {
   if (protocol === "https:" || protocol === "wss:") return "443";
   if (protocol === "socks5:") return "1080";
@@ -35,13 +52,28 @@ function normalizePort(port, protocol) {
   return String(parsed);
 }
 
+/**
+ * Build a proxy URL string manually from parsed URL components.
+ * We cannot use URL.toString() because the URL serializer silently strips
+ * default ports (80 for http, 443 for https). Proxy servers commonly
+ * listen on these ports, so we must always include the port explicitly.
+ */
+function buildProxyUrlString(parsed, port) {
+  const auth =
+    parsed.username
+      ? `${parsed.username}${parsed.password ? `:${parsed.password}` : ""}@`
+      : "";
+  return `${parsed.protocol}//${auth}${parsed.hostname}:${port}`;
+}
+
 export function isSocks5ProxyEnabled() {
   return process.env.ENABLE_SOCKS5_PROXY === "true";
 }
 
 export function proxyUrlForLogs(proxyUrl) {
+  const explicitPort = extractExplicitPort(proxyUrl);
   const parsed = new URL(proxyUrl);
-  const port = parsed.port || defaultPortForProtocol(parsed.protocol);
+  const port = explicitPort || parsed.port || defaultPortForProtocol(parsed.protocol);
   return `${parsed.protocol}//${parsed.hostname}:${port}`;
 }
 
@@ -50,6 +82,11 @@ export function normalizeProxyUrl(
   source = "proxy",
   { allowSocks5 = isSocks5ProxyEnabled() } = {}
 ) {
+  // Extract the explicit port from the raw URL string BEFORE parsing,
+  // because `new URL()` silently strips default ports (80 for http,
+  // 443 for https), which are valid and common for proxy servers.
+  const explicitPort = extractExplicitPort(proxyUrl);
+
   let parsed;
   try {
     parsed = new URL(proxyUrl);
@@ -71,8 +108,12 @@ export function normalizeProxyUrl(
     throw new Error(`[ProxyDispatcher] Invalid ${source} host`);
   }
 
-  parsed.port = normalizePort(parsed.port, parsed.protocol);
-  return parsed.toString();
+  // Use the explicit port from the raw string if present, otherwise apply default.
+  const port = explicitPort || normalizePort(parsed.port, parsed.protocol);
+
+  // Build the URL string manually instead of using parsed.toString(),
+  // which would strip default ports (80/443) and break the proxy connection.
+  return buildProxyUrlString(parsed, port);
 }
 
 export function proxyConfigToUrl(proxyConfig, { allowSocks5 = isSocks5ProxyEnabled() } = {}) {
@@ -102,14 +143,15 @@ export function proxyConfigToUrl(proxyConfig, { allowSocks5 = isSocks5ProxyEnabl
   }
 
   const port = normalizePort(proxyConfig.port, protocol);
-  const proxyUrl = new URL(`${type}://${proxyConfig.host}:${port}`);
 
-  if (proxyConfig.username) {
-    proxyUrl.username = encodeURIComponent(proxyConfig.username);
-    proxyUrl.password = proxyConfig.password ? encodeURIComponent(proxyConfig.password) : "";
-  }
+  // Build the URL string manually to preserve the port through normalization.
+  const auth = proxyConfig.username
+    ? `${encodeURIComponent(proxyConfig.username)}:${proxyConfig.password ? encodeURIComponent(proxyConfig.password) : ""}@`
+    : "";
 
-  return normalizeProxyUrl(proxyUrl.toString(), "context proxy", { allowSocks5 });
+  const proxyUrlStr = `${type}://${auth}${proxyConfig.host}:${port}`;
+
+  return normalizeProxyUrl(proxyUrlStr, "context proxy", { allowSocks5 });
 }
 
 export function createProxyDispatcher(proxyUrl) {
@@ -120,11 +162,14 @@ export function createProxyDispatcher(proxyUrl) {
   if (dispatcher) return dispatcher;
 
   const parsed = new URL(normalizedUrl);
+  const explicitPort = extractExplicitPort(normalizedUrl);
+  const port = explicitPort || normalizePort(parsed.port, parsed.protocol);
+
   if (parsed.protocol === "socks5:") {
     const socksOptions: Record<string, any> = {
       type: 5,
       host: parsed.hostname,
-      port: Number(normalizePort(parsed.port, parsed.protocol)),
+      port: Number(port),
     };
     if (parsed.username) socksOptions.userId = decodeURIComponent(parsed.username);
     if (parsed.password) socksOptions.password = decodeURIComponent(parsed.password);
@@ -135,4 +180,4 @@ export function createProxyDispatcher(proxyUrl) {
 
   dispatcherCache.set(normalizedUrl, dispatcher);
   return dispatcher;
-}
+}
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