diff --git a/packages/oauth-client/src/__tests__/session.test.ts b/packages/oauth-client/src/__tests__/session.test.ts
--- a/packages/oauth-client/src/__tests__/session.test.ts
+++ b/packages/oauth-client/src/__tests__/session.test.ts
@@ -8,7 +8,7 @@ { name: "ECDSA", namedCurve: "P-256" },
     true,
     ["sign", "verify"],
   );
-  return WebcryptoKey.fromKeypair(keyPair);
+  return WebcryptoKey.fromKeypair(keyPair, crypto.randomUUID());
 }
 
 function createSession(overrides?: {
diff --git a/packages/oauth-client/src/import-jwk.ts b/packages/oauth-client/src/import-jwk.ts
--- a/packages/oauth-client/src/import-jwk.ts
+++ b/packages/oauth-client/src/import-jwk.ts
@@ -23,5 +23,6 @@ true,
     ["verify"],
   );
 
-  return WebcryptoKey.fromKeypair({ privateKey, publicKey });
+  const kid = (jwk as JsonWebKey & { kid?: string }).kid ?? crypto.randomUUID();
+  return WebcryptoKey.fromKeypair({ privateKey, publicKey }, kid);
 }