diff --git a/scripts/lib/managed-pe-fixture.d.mts b/scripts/lib/managed-pe-fixture.d.mts
new file mode 100644
index 000000000..57567b917
--- /dev/null
+++ b/scripts/lib/managed-pe-fixture.d.mts
@@ -0,0 +1,36 @@
+export interface ManagedPeFixtureMethod {
+  readonly body?: Buffer;
+  readonly flags?: number;
+  readonly implFlags?: number;
+  readonly name: string;
+}
+
+export interface ManagedPeFixtureOptions {
+  readonly cliFlags?: number;
+  readonly corruptMetadataSignature?: boolean;
+  readonly fieldName?: string;
+  readonly ilBody?: Buffer;
+  readonly machine?: number;
+  readonly metadataValidMaskExtra?: bigint;
+  readonly methodImplFlags?: number;
+  readonly methodName?: string;
+  readonly methods?: readonly ManagedPeFixtureMethod[];
+  readonly mvid?: Buffer;
+  readonly pinvoke?: {
+    readonly importName?: string;
+    readonly mappingFlags?: number;
+    readonly moduleName?: string;
+  };
+  readonly readyToRun?: boolean;
+  readonly references?: readonly string[];
+  readonly resourceData?: Buffer;
+  readonly targetFramework?: string;
+  readonly typeName?: string;
+  readonly typeNamespace?: string;
+}
+
+export const alternateMvid: Buffer;
+export function buildManagedPeFixture(
+  options?: ManagedPeFixtureOptions,
+): Buffer;
+export function buildNativePeFixture(): Buffer;
diff --git a/scripts/lib/managed-pe-fixture.mjs b/scripts/lib/managed-pe-fixture.mjs
index dffc742f9..01d388dde 100644
--- a/scripts/lib/managed-pe-fixture.mjs
+++ b/scripts/lib/managed-pe-fixture.mjs
@@ -330,22 +330,27 @@ export const buildManagedPeFixture = (options = {}) => {
   image.writeUInt32LE(0x80, 0x3c);
   image.writeUInt32LE(0x0000_4550, 0x80);
   const coff = 0x84;
-  image.writeUInt16LE(options.machine ?? 0x014c, coff);
+  const machine = options.machine ?? 0x014c;
+  const pe32Plus = machine === 0x8664 || machine === 0xaa64;
+  const optionalSize = pe32Plus ? 0x00f0 : 0x00e0;
+  const directoryOffset = pe32Plus ? 112 : 96;
+  image.writeUInt16LE(machine, coff);
   image.writeUInt16LE(1, coff + 2);
-  image.writeUInt16LE(0x00e0, coff + 16);
+  image.writeUInt16LE(optionalSize, coff + 16);
   image.writeUInt16LE(0x0102, coff + 18);
   const optional = coff + 20;
-  image.writeUInt16LE(0x010b, optional);
+  image.writeUInt16LE(pe32Plus ? 0x020b : 0x010b, optional);
   image.writeUInt32LE(0x2000, optional + 20);
-  image.writeUInt32LE(0x0040_0000, optional + 28);
+  if (pe32Plus) image.writeBigUInt64LE(0x0040_0000n, optional + 24);
+  else image.writeUInt32LE(0x0040_0000, optional + 28);
   image.writeUInt32LE(0x1000, optional + 32);
   image.writeUInt32LE(0x200, optional + 36);
   image.writeUInt32LE(0x3000, optional + 56);
   image.writeUInt32LE(0x200, optional + 60);
-  image.writeUInt32LE(16, optional + 92);
-  image.writeUInt32LE(0x2000, optional + 96 + 14 * 8);
-  image.writeUInt32LE(72, optional + 96 + 14 * 8 + 4);
-  const section = optional + 0x00e0;
+  image.writeUInt32LE(16, optional + directoryOffset - 4);
+  image.writeUInt32LE(0x2000, optional + directoryOffset + 14 * 8);
+  image.writeUInt32LE(72, optional + directoryOffset + 14 * 8 + 4);
+  const section = optional + optionalSize;
   image.write(".text\0\0\0", section, "ascii");
   image.writeUInt32LE(0x1000, section + 8);
   image.writeUInt32LE(0x2000, section + 12);
diff --git a/tests/managedConformanceFixture.test.ts b/tests/managedConformanceFixture.test.ts
new file mode 100644
index 000000000..ec2528dc2
--- /dev/null
+++ b/tests/managedConformanceFixture.test.ts
@@ -0,0 +1,36 @@
+import { mkdtemp, rm, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+import { afterEach, describe, expect, it } from "vitest";
+
+import { buildManagedPeFixture } from "../scripts/lib/managed-pe-fixture.mjs";
+import { parseBinaryTarget } from "../src/domain/binaryTarget.js";
+
+const workspaces: string[] = [];
+
+afterEach(async () => {
+  await Promise.all(
+    workspaces.splice(0).map((path) => rm(path, { recursive: true })),
+  );
+});
+
+describe("managed conformance fixture", () => {
+  it("emits PE32+ headers when the COFF machine is x86-64", async () => {
+    const workspace = await mkdtemp(join(tmpdir(), "rea-managed-fixture-"));
+    workspaces.push(workspace);
+    const path = join(workspace, "fixture.exe");
+    await writeFile(path, buildManagedPeFixture({ machine: 0x8664 }));
+
+    const parsed = await parseBinaryTarget(path);
+
+    expect(parsed).toMatchObject({
+      ok: true,
+      value: {
+        format: "pe",
+        architecture: "x86_64",
+        managed: true,
+      },
+    });
+  });
+});