diff --git a/spec/unit/rust-crypto/rust-crypto.spec.ts b/spec/unit/rust-crypto/rust-crypto.spec.ts
index 1e617c22d..85c18af1a 100644
--- a/spec/unit/rust-crypto/rust-crypto.spec.ts
+++ b/spec/unit/rust-crypto/rust-crypto.spec.ts
@@ -26,9 +26,10 @@ import { IHttpOpts, IToDeviceEvent, MatrixClient, MatrixHttpApi } from "../../..
 import { mkEvent } from "../../test-utils/test-utils";
 import { CryptoBackend } from "../../../src/common-crypto/CryptoBackend";
 import { IEventDecryptionResult } from "../../../src/@types/crypto";
-import { OutgoingRequestProcessor } from "../../../src/rust-crypto/OutgoingRequestProcessor";
+import { OutgoingRequest, OutgoingRequestProcessor } from "../../../src/rust-crypto/OutgoingRequestProcessor";
 import { ServerSideSecretStorage } from "../../../src/secret-storage";
 import { ImportRoomKeysOpts } from "../../../src/crypto-api";
+import * as testData from "../../test-utils/test-data";
 
 afterEach(() => {
     // reset fake-indexeddb after each test, to make sure we don't leak connections
@@ -357,6 +358,35 @@ describe("RustCrypto", () => {
         });
     });
 
+    describe("userHasCrossSigningKeys", () => {
+        let rustCrypto: RustCrypto;
+
+        beforeEach(async () => {
+            rustCrypto = await makeTestRustCrypto(undefined, testData.TEST_USER_ID);
+        });
+
+        it("returns false if there is no cross-signing identity", async () => {
+            await expect(rustCrypto.userHasCrossSigningKeys()).resolves.toBe(false);
+        });
+
+        it("returns true if OlmMachine has a cross-signing identity", async () => {
+            // @ts-ignore private field
+            const olmMachine = rustCrypto.olmMachine;
+
+            const outgoingRequests: OutgoingRequest[] = await olmMachine.outgoingRequests();
+            // pick out the KeysQueryRequest, and respond to it with the cross-signing keys
+            const req = outgoingRequests.find((r) => r instanceof KeysQueryRequest)!;
+            await olmMachine.markRequestAsSent(
+                req.id!,
+                req.type,
+                JSON.stringify(testData.SIGNED_CROSS_SIGNING_KEYS_DATA),
+            );
+
+            // ... and we should now have cross-signing keys.
+            await expect(rustCrypto.userHasCrossSigningKeys()).resolves.toBe(true);
+        });
+    });
+
     describe("createRecoveryKeyFromPassphrase", () => {
         let rustCrypto: RustCrypto;
 
diff --git a/src/rust-crypto/rust-crypto.ts b/src/rust-crypto/rust-crypto.ts
index 84a21c548..0405ed429 100644
--- a/src/rust-crypto/rust-crypto.ts
+++ b/src/rust-crypto/rust-crypto.ts
@@ -188,9 +188,12 @@ export class RustCrypto implements CryptoBackend {
 
     public globalBlacklistUnverifiedDevices = false;
 
+    /**
+     * Implementation of {@link CryptoApi.userHasCrossSigningKeys}.
+     */
     public async userHasCrossSigningKeys(): Promise<boolean> {
-        // TODO
-        return false;
+        const userIdentity = await this.olmMachine.getIdentity(new RustSdkCryptoJs.UserId(this.userId));
+        return userIdentity !== undefined;
     }
 
     public prepareToEncrypt(room: Room): void {