diff --git a/frontend/src/lib/gateway-form.test.ts b/frontend/src/lib/gateway-form.test.ts
index e2803eca..63fa4a59 100644
--- a/frontend/src/lib/gateway-form.test.ts
+++ b/frontend/src/lib/gateway-form.test.ts
@@ -13,14 +13,66 @@ const mockedGatewaysStatusApiV1GatewaysStatusGet = vi.mocked(
 );
 
 describe("validateGatewayUrl", () => {
-  it("requires ws/wss with an explicit port", () => {
-    expect(validateGatewayUrl("https://gateway.example")).toBe(
-      "Gateway URL must start with ws:// or wss://.",
-    );
-    expect(validateGatewayUrl("ws://gateway.example")).toBe(
+  it("accepts ws:// with explicit non-default port", () => {
+    expect(validateGatewayUrl("ws://localhost:18789")).toBeNull();
+  });
+
+  it("accepts wss:// with explicit non-default port", () => {
+    expect(validateGatewayUrl("wss://gateway.example.com:8443")).toBeNull();
+  });
+
+  it("accepts wss:// with explicit default port 443", () => {
+    expect(validateGatewayUrl("wss://devbot.tailcc2080.ts.net:443")).toBeNull();
+  });
+
+  it("accepts ws:// with explicit default port 80", () => {
+    expect(validateGatewayUrl("ws://localhost:80")).toBeNull();
+  });
+
+  it("accepts URLs with a path after the port", () => {
+    expect(validateGatewayUrl("wss://host.example.com:443/gateway")).toBeNull();
+  });
+
+  it("trims surrounding whitespace before validating", () => {
+    expect(validateGatewayUrl("  wss://host:443  ")).toBeNull();
+  });
+
+  it("rejects empty string", () => {
+    expect(validateGatewayUrl("")).toBe("Gateway URL is required.");
+  });
+
+  it("rejects wss:// with no port at all", () => {
+    expect(validateGatewayUrl("wss://gateway.example.com")).toBe(
       "Gateway URL must include an explicit port.",
     );
-    expect(validateGatewayUrl("ws://gateway.example:18789")).toBeNull();
+  });
+
+  it("rejects ws:// with no port at all", () => {
+    expect(validateGatewayUrl("ws://localhost")).toBe(
+      "Gateway URL must include an explicit port.",
+    );
+  });
+
+  it("rejects https:// scheme", () => {
+    expect(validateGatewayUrl("https://gateway.example.com:443")).toBe(
+      "Gateway URL must start with ws:// or wss://.",
+    );
+  });
+
+  it("rejects http:// scheme", () => {
+    expect(validateGatewayUrl("http://localhost:8080")).toBe(
+      "Gateway URL must start with ws:// or wss://.",
+    );
+  });
+
+  it("rejects completely invalid URL", () => {
+    expect(validateGatewayUrl("not-a-url")).toBe(
+      "Enter a valid gateway URL including port.",
+    );
+  });
+
+  it("rejects URL with only whitespace", () => {
+    expect(validateGatewayUrl("   ")).toBe("Gateway URL is required.");
   });
 });
 
diff --git a/frontend/src/lib/gateway-form.ts b/frontend/src/lib/gateway-form.ts
index e247f39e..e3a48846 100644
--- a/frontend/src/lib/gateway-form.ts
+++ b/frontend/src/lib/gateway-form.ts
@@ -4,6 +4,30 @@ export const DEFAULT_WORKSPACE_ROOT = "~/.openclaw";
 
 export type GatewayCheckStatus = "idle" | "checking" | "success" | "error";
 
+/**
+ * Returns true only when the URL string contains an explicit ":port" segment.
+ *
+ * JavaScript's URL API sets `.port` to "" for *both* an omitted port and a
+ * port that equals the scheme's default (e.g. 443 for wss:). We therefore
+ * inspect the raw host+port token from the URL string instead.
+ */
+function hasExplicitPort(urlString: string): boolean {
+  try {
+    const { hostname } = new URL(urlString);
+    // Extract the authority portion (between // and the first / ? or #)
+    const withoutScheme = urlString.slice(urlString.indexOf("//") + 2);
+    const authority = withoutScheme.split(/[/?#]/)[0];
+    // authority is either "host", "host:port", or "[ipv6]:port"
+    // Remove a leading IPv6 bracket group before checking for ":"
+    const withoutIPv6 = authority.startsWith("[")
+      ? authority.slice(authority.indexOf("]") + 1)
+      : authority.slice(hostname.length);
+    return withoutIPv6.startsWith(":") && /^:\d+$/.test(withoutIPv6);
+  } catch {
+    return false;
+  }
+}
+
 export const validateGatewayUrl = (value: string) => {
   const trimmed = value.trim();
   if (!trimmed) return "Gateway URL is required.";
@@ -12,10 +36,7 @@ export const validateGatewayUrl = (value: string) => {
     if (url.protocol !== "ws:" && url.protocol !== "wss:") {
       return "Gateway URL must start with ws:// or wss://.";
     }
-    // url.port is empty for default ports (80 for ws:, 443 for wss:) — allow those
-    const defaultPorts: Record<string, string> = { "ws:": "80", "wss:": "443" };
-    const effectivePort = url.port || defaultPorts[url.protocol] || "";
-    if (!effectivePort) {
+    if (!hasExplicitPort(trimmed)) {
       return "Gateway URL must include an explicit port.";
     }
     return null;