diff --git a/src/domain/peOptionalHeader.ts b/src/domain/peOptionalHeader.ts
index b65e706ced..4500b288b5 100644
--- a/src/domain/peOptionalHeader.ts
+++ b/src/domain/peOptionalHeader.ts
@@ -8,11 +8,14 @@ export interface PeDataDirectory {
   readonly offset: number;
 }
 
-/** Structural facts copied from one declared PE optional header. */
-export interface PeOptionalHeaderFixedFields {
+export interface PeOptionalHeaderIdentity {
   readonly magic: 0x10b | 0x20b;
   readonly bits: 32 | 64;
   readonly format: "pe32" | "pe32-plus";
+}
+
+/** Structural facts copied from one declared PE optional header. */
+export interface PeOptionalHeaderFixedFields extends PeOptionalHeaderIdentity {
   readonly imageBase: bigint;
   readonly sectionAlignment: number;
   readonly fileAlignment: number;
@@ -37,10 +40,10 @@ export interface PeOptionalHeaderFailure {
   readonly message: string;
 }
 
-/** Decode mapping fields without requiring a directory count or table. */
-export const readPeOptionalHeaderFixedFields = (
+/** Decode format identity without requiring mapping fields or directories. */
+export const readPeOptionalHeaderIdentity = (
   bytes: Uint8Array,
-): Result<PeOptionalHeaderFixedFields, PeOptionalHeaderFailure> => {
+): Result<PeOptionalHeaderIdentity, PeOptionalHeaderFailure> => {
   if (bytes.byteLength < 2)
     return err({
       kind: "malformed",
@@ -56,6 +59,16 @@ export const readPeOptionalHeaderFixedFields = (
       message: "Only PE32 and PE32+ image optional headers are supported",
     });
   const bits = magic === 0x20b ? 64 : 32;
+  return ok({ magic, bits, format: bits === 64 ? "pe32-plus" : "pe32" });
+};
+
+/** Decode mapping fields without requiring a directory count or table. */
+export const readPeOptionalHeaderFixedFields = (
+  bytes: Uint8Array,
+): Result<PeOptionalHeaderFixedFields, PeOptionalHeaderFailure> => {
+  const identity = readPeOptionalHeaderIdentity(bytes);
+  if (!identity.ok) return identity;
+  const { bits } = identity.value;
   const directoryOffset = bits === 64 ? 112 : 96;
   if (bytes.byteLength < 64)
     return err({
@@ -63,10 +76,9 @@ export const readPeOptionalHeaderFixedFields = (
       reason: "truncated-fixed-fields",
       message: "truncated PE optional header",
     });
+  const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
   return ok({
-    magic,
-    bits,
-    format: bits === 64 ? "pe32-plus" : "pe32",
+    ...identity.value,
     imageBase:
       bits === 64
         ? view.getBigUint64(24, true)
diff --git a/src/domain/windowsNativeArtifact.test.ts b/src/domain/windowsNativeArtifact.test.ts
index 248469d7a7..e7bc10621f 100644
--- a/src/domain/windowsNativeArtifact.test.ts
+++ b/src/domain/windowsNativeArtifact.test.ts
@@ -7,11 +7,12 @@ import {
 } from "./windowsNativeArtifact.js";
 
 const fixture = () => {
-  const bytes = Buffer.alloc(128);
+  const bytes = Buffer.alloc(152);
   bytes.write("MZ");
   bytes.writeUInt32LE(64, 0x3c);
   bytes.write("PE\0\0", 64, "ascii");
   bytes.writeUInt16LE(0x8664, 68);
+  bytes.writeUInt16LE(64, 84);
   bytes.writeUInt16LE(0x20b, 88);
   const manifest = {
     packageVersion: "1.0.0",
@@ -116,3 +117,26 @@ it.each(["offset", "signature", "machine", "optional magic"])(
     });
   },
 );
+
+it.each([0, 1, 65, 0xffff])(
+  "rejects an unavailable declared optional header of %i bytes",
+  (length) => {
+    const { bytes } = fixture();
+    bytes.writeUInt16LE(length, 84);
+    expect(createWindowsNativeManifest("1.0.0", bytes)).toMatchObject({
+      ok: false,
+      error: { message: expect.stringContaining("PE32+") },
+    });
+  },
+);
+
+it.each([2, 32, 63, 64])(
+  "admits PE32+ identity in a present declared header of %i bytes",
+  (length) => {
+    const { bytes } = fixture();
+    bytes.writeUInt16LE(length, 84);
+    expect(createWindowsNativeManifest("1.0.0", bytes)).toMatchObject({
+      ok: true,
+    });
+  },
+);
diff --git a/src/domain/windowsNativeArtifact.ts b/src/domain/windowsNativeArtifact.ts
index 0412340549..cdb943cbec 100644
--- a/src/domain/windowsNativeArtifact.ts
+++ b/src/domain/windowsNativeArtifact.ts
@@ -1,6 +1,7 @@
 import { observeMzWindowsHeader } from "./dosMz.js";
 import { createHash } from "node:crypto";
 import { readPeCoffHeader } from "./peCoffHeader.js";
+import { readPeOptionalHeaderIdentity } from "./peOptionalHeader.js";
 import { err, ok, type Result } from "./result.js";
 
 /** Fixed compatibility contract shared by the artifact producer and readers. */
@@ -99,14 +100,21 @@ const validateWindowsX64Artifact = (
       ),
     );
   const offset = observed.offset;
-  if (offset > bytes.length - 26 || bytes.readUInt16LE(offset + 24) !== 0x20b)
+  const coff = readPeCoffHeader(bytes.subarray(offset + 4, offset + 24));
+  if (
+    !coff.ok ||
+    coff.value.machine !== 0x8664 ||
+    coff.value.optionalHeaderSize > bytes.length - offset - 24
+  )
     return err(
       new WindowsNativeArtifactError(
         "Windows native artifact is not a Windows x64 PE32+ image",
       ),
     );
-  const coff = readPeCoffHeader(bytes.subarray(offset + 4, offset + 24));
-  if (!coff.ok || coff.value.machine !== 0x8664)
+  const optional = readPeOptionalHeaderIdentity(
+    bytes.subarray(offset + 24, offset + 24 + coff.value.optionalHeaderSize),
+  );
+  if (!optional.ok || optional.value.bits !== 64)
     return err(
       new WindowsNativeArtifactError(
         "Windows native artifact is not a Windows x64 PE32+ image",