diff --git a/.changeset/wild-steaks-bathe.md b/.changeset/wild-steaks-bathe.md
new file mode 100644
index 00000000000..25a35dce28b
--- /dev/null
+++ b/.changeset/wild-steaks-bathe.md
@@ -0,0 +1,7 @@
+---
+"@remix-run/dev": patch
+---
+
+Fix server builds where serverBuildPath extension is `.cjs`.
+
+Fix a bug that caused the server build file to be emitted into the assets directory if the value of `serverBuildPath` ended in `.cjs`.
diff --git a/integration/compiler-mjs-cjs-output-test.ts b/integration/compiler-mjs-cjs-output-test.ts
new file mode 100644
index 00000000000..86b03edd7a3
--- /dev/null
+++ b/integration/compiler-mjs-cjs-output-test.ts
@@ -0,0 +1,35 @@
+import { test, expect } from "@playwright/test";
+import * as fs from "node:fs";
+import * as path from "node:path";
+
+import { createFixtureProject, js } from "./helpers/create-fixture.js";
+
+test.describe("", () => {
+  for (let [serverModuleExt, serverModuleFormat, exportStatement] of [
+    ["mjs", "esm", "export {"],
+    ["cjs", "cjs", "module.exports ="],
+  ]) {
+    test(`can write .${serverModuleExt} server output module`, async () => {
+      let projectDir = await createFixtureProject({
+        files: {
+          // Ensure the config is valid ESM
+          "remix.config.js": js`
+            export default {
+              serverModuleFormat: "${serverModuleFormat}",
+              serverBuildPath: "build/index.${serverModuleExt}",
+            };
+          `,
+        },
+      });
+
+      let buildPath = path.resolve(
+        projectDir,
+        "build",
+        `index.${serverModuleExt}`
+      );
+      expect(fs.existsSync(buildPath), "doesn't exist").toBe(true);
+      let contents = fs.readFileSync(buildPath, "utf8");
+      expect(contents, "no export statement").toContain(exportStatement);
+    });
+  }
+});
diff --git a/integration/compiler-mjs-output-test.ts b/integration/compiler-mjs-output-test.ts
deleted file mode 100644
index 65d112ad9ea..00000000000
--- a/integration/compiler-mjs-output-test.ts
+++ /dev/null
@@ -1,69 +0,0 @@
-import { test, expect } from "@playwright/test";
-import * as fs from "node:fs";
-import * as path from "node:path";
-
-import { createFixtureProject, js, json } from "./helpers/create-fixture.js";
-
-let projectDir: string;
-
-test.beforeAll(async () => {
-  projectDir = await createFixtureProject({
-    files: {
-      // Ensure the config is valid ESM
-      "remix.config.js": js`
-        export default {
-          serverModuleFormat: "esm",
-          serverBuildPath: "build/index.mjs",
-        };
-      `,
-      "package.json": json({
-        name: "remix-template-remix",
-        private: true,
-        sideEffects: false,
-        type: "module",
-        dependencies: {
-          "@remix-run/node": "0.0.0-local-version",
-          "@remix-run/react": "0.0.0-local-version",
-          "@remix-run/serve": "0.0.0-local-version",
-          isbot: "0.0.0-local-version",
-          react: "0.0.0-local-version",
-          "react-dom": "0.0.0-local-version",
-        },
-        devDependencies: {
-          "@remix-run/dev": "0.0.0-local-version",
-          "@types/react": "0.0.0-local-version",
-          "@types/react-dom": "0.0.0-local-version",
-          typescript: "0.0.0-local-version",
-        },
-        engines: {
-          node: ">=18.0.0",
-        },
-      }),
-      "app/routes/_index.tsx": js`
-        import { json } from "@remix-run/node";
-        import { useLoaderData, Link } from "@remix-run/react";
-
-        export function loader() {
-          return json("pizza");
-        }
-
-        export default function Index() {
-          let data = useLoaderData();
-          return (
-            <div>
-              {data}
-              <Link to="/burgers">Other Route</Link>
-            </div>
-          )
-        }
-      `,
-    },
-  });
-});
-
-test("can write .mjs server output module", () => {
-  let buildPath = path.resolve(projectDir, "build", "index.mjs");
-  expect(fs.existsSync(buildPath), "doesn't exist").toBe(true);
-  let contents = fs.readFileSync(buildPath, "utf8");
-  expect(contents, "no export statement").toContain("export {");
-});
diff --git a/packages/remix-dev/compiler/server/write.ts b/packages/remix-dev/compiler/server/write.ts
index 948d1a0b5a4..d5300452d1b 100644
--- a/packages/remix-dev/compiler/server/write.ts
+++ b/packages/remix-dev/compiler/server/write.ts
@@ -11,7 +11,7 @@ export async function write(
   await fse.ensureDir(path.dirname(config.serverBuildPath));
 
   for (let file of outputFiles) {
-    if (file.path.endsWith(".js") || file.path.endsWith(".mjs")) {
+    if ([".js", ".cjs", ".mjs"].some((ext) => file.path.endsWith(ext))) {
       // fix sourceMappingURL to be relative to current path instead of /build
       let filename = file.path.substring(file.path.lastIndexOf(path.sep) + 1);
       let escapedFilename = filename.replace(/\./g, "\\.");