diff --git a/.changeset/wise-quokkas-hop.md b/.changeset/wise-quokkas-hop.md
new file mode 100644
index 000000000..89c2b840d
--- /dev/null
+++ b/.changeset/wise-quokkas-hop.md
@@ -0,0 +1,9 @@
+---
+"@opennextjs/cloudflare": patch
+---
+
+Fix `copyWorkerdPackages` on Windows so packages listed in `serverExternalPackages` are correctly identified and their `workerd`-condition files (e.g. `web.mjs`) end up in the bundle.
+
+The package name was extracted from a `node_modules/...` path with the platform's native separator. On Windows that produced `@scope\name`, which never matched the forward-slash entries in `serverExternalPackages`, so the workerd-condition copy was silently skipped and downstream esbuild would fail with `Could not resolve` errors (e.g. for `@libsql/isomorphic-ws` → `./web.mjs`).
+
+The extraction now normalizes separators and trims to the package name, so nested `package.json` paths like `@scope/pkg/lib-cjs/package.json` also resolve to `@scope/pkg`.
diff --git a/packages/cloudflare/src/cli/build/utils/workerd.spec.ts b/packages/cloudflare/src/cli/build/utils/workerd.spec.ts
index 7f64287bc..7e877896b 100644
--- a/packages/cloudflare/src/cli/build/utils/workerd.spec.ts
+++ b/packages/cloudflare/src/cli/build/utils/workerd.spec.ts
@@ -1,6 +1,6 @@
 import { describe, expect, test } from "vitest";
 
-import { transformBuildCondition, transformPackageJson } from "./workerd.js";
+import { extractExternalPackageName, transformBuildCondition, transformPackageJson } from "./workerd.js";
 
 describe("transformBuildCondition", () => {
 	test("top level", () => {
@@ -254,3 +254,41 @@ describe("transformPackageJson", () => {
 		expect(hasBuildCondition).toBe(true);
 	});
 });
+
+describe("extractExternalPackageName", () => {
+	test("scoped package on posix", () => {
+		expect(extractExternalPackageName("/app/node_modules/@libsql/isomorphic-ws")).toBe(
+			"@libsql/isomorphic-ws"
+		);
+	});
+
+	test("unscoped package on posix", () => {
+		expect(extractExternalPackageName("/app/node_modules/ws")).toBe("ws");
+	});
+
+	test("scoped package on windows", () => {
+		expect(extractExternalPackageName("F:\\app\\node_modules\\@libsql\\isomorphic-ws")).toBe(
+			"@libsql/isomorphic-ws"
+		);
+	});
+
+	test("unscoped package on windows", () => {
+		expect(extractExternalPackageName("F:\\app\\node_modules\\ws")).toBe("ws");
+	});
+
+	test("trims nested subpath to the package name (posix)", () => {
+		expect(extractExternalPackageName("/app/node_modules/@libsql/hrana-client/lib-cjs")).toBe(
+			"@libsql/hrana-client"
+		);
+	});
+
+	test("trims nested subpath to the package name (windows)", () => {
+		expect(extractExternalPackageName("F:\\app\\node_modules\\@libsql\\hrana-client\\lib-cjs")).toBe(
+			"@libsql/hrana-client"
+		);
+	});
+
+	test("returns undefined when the path is not under node_modules", () => {
+		expect(extractExternalPackageName("/app/src/lib/foo.ts")).toBeUndefined();
+	});
+});
diff --git a/packages/cloudflare/src/cli/build/utils/workerd.ts b/packages/cloudflare/src/cli/build/utils/workerd.ts
index e5010740a..e38993f91 100644
--- a/packages/cloudflare/src/cli/build/utils/workerd.ts
+++ b/packages/cloudflare/src/cli/build/utils/workerd.ts
@@ -76,9 +76,27 @@ export function transformPackageJson(json: PackageJson) {
 	return { transformed, hasBuildCondition };
 }
 
-export async function copyWorkerdPackages(options: BuildOptions, nodePackages: Map<string, string>) {
-	const isNodeModuleRegex = getCrossPlatformPathRegex(`.*/node_modules/(?<pkg>.*)`, { escape: false });
+const NODE_MODULES_PATH_REGEX = getCrossPlatformPathRegex(`.*/node_modules/(?<pkg>.*)`, { escape: false });
+
+/**
+ * Extracts the npm package name from a path inside `node_modules`.
+ *
+ * Normalizes Windows backslashes to POSIX separators so the result can be
+ * compared against `serverExternalPackages` entries (which always use `/`).
+ * Trims back to the package name proper, so nested `package.json` files
+ * (e.g. `@scope/pkg/lib-cjs/package.json`) return `@scope/pkg`.
+ *
+ * @returns The package name, or `undefined` if `src` is not under `node_modules`.
+ */
+export function extractExternalPackageName(src: string): string | undefined {
+	const match = src.match(NODE_MODULES_PATH_REGEX);
+	const raw = match?.groups?.pkg;
+	if (!raw) return undefined;
+	const parts = raw.replaceAll("\\", "/").split("/");
+	return parts[0]?.startsWith("@") ? parts.slice(0, 2).join("/") : parts[0];
+}
 
+export async function copyWorkerdPackages(options: BuildOptions, nodePackages: Map<string, string>) {
 	// Copy full external packages when they use "workerd" build condition
 	const nextConfig = loadConfig(path.join(options.appBuildOutputPath, ".next"));
 	const externalPackages =
@@ -88,8 +106,8 @@ export async function copyWorkerdPackages(options: BuildOptions, nodePackages: M
 		try {
 			const pkgJson = JSON.parse(await fs.readFile(path.join(src, "package.json"), "utf8"));
 			const { transformed, hasBuildCondition } = transformPackageJson(pkgJson);
-			const match = src.match(isNodeModuleRegex);
-			if (match?.groups?.pkg && externalPackages.includes(match.groups.pkg) && hasBuildCondition) {
+			const pkg = extractExternalPackageName(src);
+			if (pkg && externalPackages.includes(pkg) && hasBuildCondition) {
 				logger.debug(
 					`Copying package using a workerd condition: ${path.relative(options.appPath, src)} -> ${path.relative(options.appPath, dst)}`
 				);