diff --git a/packages/hdwallet-keepkey/src/keepkey-initialize.test.ts b/packages/hdwallet-keepkey/src/keepkey-initialize.test.ts
new file mode 100644
index 00000000..0f872fb1
--- /dev/null
+++ b/packages/hdwallet-keepkey/src/keepkey-initialize.test.ts
@@ -0,0 +1,89 @@
+/**
+ * Unit tests for KeepKeyHDWallet.initialize() version-field validation.
+ *
+ * Regression: when transport.call() returns a Features payload missing
+ * majorVersion / minorVersion / patchVersion (e.g. wrong message type
+ * miscast, decode mismatch, or device in an unexpected state), the prior
+ * code constructed `vundefined.undefined.undefined` and called
+ * semver.gte() on it, which threw the opaque error
+ *   "Invalid Version: vundefined.undefined.undefined"
+ * leaking from the WebUSB pair path with no actionable diagnostic.
+ *
+ * The fix throws a clear error before reaching semver.
+ */
+import { KeepKeyHDWallet } from "./keepkey";
+
+function makeMockTransport(callResponse: any) {
+  return {
+    debugLink: false,
+    call: jest.fn().mockResolvedValue(callResponse),
+    getDeviceID: jest.fn().mockResolvedValue("mock-device-id"),
+    keyring: { addAlias: jest.fn() },
+  } as any;
+}
+
+describe("KeepKeyHDWallet.initialize() version-field validation", () => {
+  it("throws a clear error when Features has no version fields", async () => {
+    const transport = makeMockTransport({
+      message: {
+        deviceId: "mock-device-id",
+        // majorVersion / minorVersion / patchVersion intentionally absent
+      },
+    });
+    const wallet = new KeepKeyHDWallet(transport);
+
+    const err = await wallet.initialize().catch((e: any) => e);
+    expect(err).toBeInstanceOf(Error);
+    expect(err.message).toMatch(/KeepKey Initialize returned Features without firmware version/);
+    expect(err.message).toMatch(/major=undefined, minor=undefined, patch=undefined/);
+  });
+
+  it("throws when only majorVersion is missing", async () => {
+    const transport = makeMockTransport({
+      message: {
+        deviceId: "mock-device-id",
+        minorVersion: 14,
+        patchVersion: 0,
+      },
+    });
+    const wallet = new KeepKeyHDWallet(transport);
+    await expect(wallet.initialize()).rejects.toThrow(
+      /KeepKey Initialize returned Features without firmware version/
+    );
+  });
+
+  it("resolves successfully when all version fields are present", async () => {
+    const transport = makeMockTransport({
+      message: {
+        deviceId: "mock-device-id",
+        majorVersion: 7,
+        minorVersion: 14,
+        patchVersion: 0,
+      },
+    });
+    const wallet = new KeepKeyHDWallet(transport);
+
+    const features = await wallet.initialize();
+    expect(features).toBeDefined();
+    expect(features.majorVersion).toBe(7);
+    expect(features.minorVersion).toBe(14);
+    expect(features.patchVersion).toBe(0);
+  });
+
+  it("regression: never produces 'Invalid Version: vundefined.undefined.undefined'", async () => {
+    const transport = makeMockTransport({
+      message: { deviceId: "mock-device-id" },
+    });
+    const wallet = new KeepKeyHDWallet(transport);
+    let err: any;
+    try {
+      await wallet.initialize();
+    } catch (e) {
+      err = e;
+    }
+    expect(err).toBeDefined();
+    expect(String(err.message ?? err)).not.toMatch(
+      /Invalid Version: vundefined\.undefined\.undefined/
+    );
+  });
+});
diff --git a/packages/hdwallet-keepkey/src/keepkey.ts b/packages/hdwallet-keepkey/src/keepkey.ts
index 4e6fd8dc..ff3aec8f 100644
--- a/packages/hdwallet-keepkey/src/keepkey.ts
+++ b/packages/hdwallet-keepkey/src/keepkey.ts
@@ -1187,6 +1187,24 @@ export class KeepKeyHDWallet implements core.HDWallet, core.BTCWallet, core.ETHW
       this.transport.keyring.addAlias(transportDeviceID, out.deviceId);
     }
 
+    // Validate version fields BEFORE constructing the semver string. Without this,
+    // a Features response missing major/minor/patch (e.g. wrong message type cast,
+    // device in an unexpected state, or runtime decode mismatch) produces
+    // `vundefined.undefined.undefined`, which semver.gte() rejects with the opaque
+    // error "Invalid Version: vundefined.undefined.undefined". Surface a clear
+    // diagnostic instead so callers can recognize the failure mode.
+    if (
+      typeof out.majorVersion !== "number" ||
+      typeof out.minorVersion !== "number" ||
+      typeof out.patchVersion !== "number"
+    ) {
+      throw new Error(
+        `KeepKey Initialize returned Features without firmware version ` +
+        `(major=${out.majorVersion}, minor=${out.minorVersion}, patch=${out.patchVersion}). ` +
+        `Device may be in bootloader mode, mid-update, or returned an unexpected message type.`
+      );
+    }
+
     const fwVersion = `v${out.majorVersion}.${out.minorVersion}.${out.patchVersion}`;
     //Lost Support per proto 44.3
     this._supportsOsmosis = semver.gte(fwVersion, "v7.7.0");