diff --git a/src/create-prompt/index.ts b/src/create-prompt/index.ts
index 66149eac3..f4a128953 100644
--- a/src/create-prompt/index.ts
+++ b/src/create-prompt/index.ts
@@ -20,6 +20,7 @@ import {
 import type { ParsedGitHubContext } from "../github/context";
 import type { CommonFields, PreparedContext, EventData } from "./types";
 import { GITHUB_SERVER_URL } from "../github/api/config";
+import { getNoreplyEmailDomain } from "../utils/noreply-email";
 import type { Mode, ModeContext } from "../modes/types";
 import { extractUserRequest } from "../utils/extract-user-request";
 export type { CommonFields, PreparedContext } from "./types";
@@ -402,9 +403,12 @@ function getCommitInstructions(
   context: PreparedContext,
   useCommitSigning: boolean,
 ): string {
+  // Determine the noreply email domain based on GITHUB_SERVER_URL (for GHES support)
+  const noreplyDomain = getNoreplyEmailDomain(GITHUB_SERVER_URL);
+
   const coAuthorLine =
     (githubData.triggerDisplayName ?? context.triggerUsername !== "Unknown")
-      ? `Co-authored-by: ${githubData.triggerDisplayName ?? context.triggerUsername} <${context.triggerUsername}@users.noreply.github.com>`
+      ? `Co-authored-by: ${githubData.triggerDisplayName ?? context.triggerUsername} <${context.triggerUsername}@${noreplyDomain}>`
       : "";
 
   if (useCommitSigning) {
diff --git a/src/github/operations/git-config.ts b/src/github/operations/git-config.ts
index 733744f51..d53f621c8 100644
--- a/src/github/operations/git-config.ts
+++ b/src/github/operations/git-config.ts
@@ -11,6 +11,7 @@ import { join } from "path";
 import { homedir } from "os";
 import type { GitHubContext } from "../context";
 import { GITHUB_SERVER_URL } from "../api/config";
+import { getNoreplyEmailDomain } from "../../utils/noreply-email";
 
 const SSH_SIGNING_KEY_PATH = join(homedir(), ".ssh", "claude_signing_key");
 
@@ -28,10 +29,7 @@ export async function configureGitAuth(
 
   // Determine the noreply email domain based on GITHUB_SERVER_URL
   const serverUrl = new URL(GITHUB_SERVER_URL);
-  const noreplyDomain =
-    serverUrl.hostname === "github.com"
-      ? "users.noreply.github.com"
-      : `users.noreply.${serverUrl.hostname}`;
+  const noreplyDomain = getNoreplyEmailDomain(GITHUB_SERVER_URL);
 
   // Configure git user
   console.log("Configuring git user...");
diff --git a/src/utils/noreply-email.ts b/src/utils/noreply-email.ts
new file mode 100644
index 000000000..98cbaf1c4
--- /dev/null
+++ b/src/utils/noreply-email.ts
@@ -0,0 +1,20 @@
+/**
+ * Utility for generating GitHub noreply email domains
+ * Handles both github.com and GitHub Enterprise Server (GHES) instances
+ */
+
+/**
+ * Get the noreply email domain for a GitHub server URL
+ *
+ * For github.com: returns "users.noreply.github.com"
+ * For GHES (e.g., ghes.example.com): returns "users.noreply.ghes.example.com"
+ *
+ * @param serverUrl - The GitHub server URL (e.g., "https://github.com" or "https://ghes.example.com")
+ * @returns The noreply email domain
+ */
+export function getNoreplyEmailDomain(serverUrl: string): string {
+  const url = new URL(serverUrl);
+  return url.hostname === "github.com"
+    ? "users.noreply.github.com"
+    : `users.noreply.${url.hostname}`;
+}
diff --git a/test/noreply-email.test.ts b/test/noreply-email.test.ts
new file mode 100644
index 000000000..e78083e73
--- /dev/null
+++ b/test/noreply-email.test.ts
@@ -0,0 +1,54 @@
+#!/usr/bin/env bun
+
+import { describe, test, expect } from "bun:test";
+import { getNoreplyEmailDomain } from "../src/utils/noreply-email";
+
+describe("getNoreplyEmailDomain", () => {
+  test("returns users.noreply.github.com for github.com", () => {
+    expect(getNoreplyEmailDomain("https://github.com")).toBe(
+      "users.noreply.github.com",
+    );
+  });
+
+  test("returns users.noreply.github.com for github.com with trailing slash", () => {
+    expect(getNoreplyEmailDomain("https://github.com/")).toBe(
+      "users.noreply.github.com",
+    );
+  });
+
+  test("returns GHES noreply domain for enterprise server", () => {
+    expect(getNoreplyEmailDomain("https://ghes.example.com")).toBe(
+      "users.noreply.ghes.example.com",
+    );
+  });
+
+  test("returns GHES noreply domain for enterprise server with trailing slash", () => {
+    expect(getNoreplyEmailDomain("https://ghes.example.com/")).toBe(
+      "users.noreply.ghes.example.com",
+    );
+  });
+
+  test("returns GHES noreply domain for enterprise server with port", () => {
+    expect(getNoreplyEmailDomain("https://ghes.example.com:8443")).toBe(
+      "users.noreply.ghes.example.com",
+    );
+  });
+
+  test("returns GHES noreply domain for enterprise server with path", () => {
+    expect(getNoreplyEmailDomain("https://ghes.example.com/api/v3")).toBe(
+      "users.noreply.ghes.example.com",
+    );
+  });
+
+  test("handles subdomain enterprise servers", () => {
+    expect(getNoreplyEmailDomain("https://github.mycompany.com")).toBe(
+      "users.noreply.github.mycompany.com",
+    );
+  });
+
+  test("handles deep subdomain enterprise servers", () => {
+    expect(getNoreplyEmailDomain("https://git.internal.corp.example.com")).toBe(
+      "users.noreply.git.internal.corp.example.com",
+    );
+  });
+});