diff --git a/src/client-side-encryption/providers/index.ts b/src/client-side-encryption/providers/index.ts
index 54f4366f6f..f254cf69f9 100644
--- a/src/client-side-encryption/providers/index.ts
+++ b/src/client-side-encryption/providers/index.ts
@@ -1,3 +1,4 @@
+import type { Binary } from '../../bson';
 import { loadAWSCredentials } from './aws';
 import { loadAzureCredentials } from './azure';
 import { loadGCPCredentials } from './gcp';
@@ -39,7 +40,7 @@ export interface LocalKMSProviderConfiguration {
    * The master key used to encrypt/decrypt data keys.
    * A 96-byte long Buffer or base64 encoded string.
    */
-  key: Buffer | string;
+  key: Binary | Uint8Array | string;
 }
 
 /** @public */
diff --git a/test/types/client-side-encryption.test-d.ts b/test/types/client-side-encryption.test-d.ts
index 53e4060aa2..87c9d46a34 100644
--- a/test/types/client-side-encryption.test-d.ts
+++ b/test/types/client-side-encryption.test-d.ts
@@ -9,7 +9,7 @@ import type {
   KMSProviders,
   RangeOptions
 } from '../..';
-import type { ClientEncryptionDataKeyProvider } from '../mongodb';
+import { Binary, type ClientEncryptionDataKeyProvider } from '../mongodb';
 
 type RequiredCreateEncryptedCollectionSettings = Parameters<
   ClientEncryption['createEncryptedCollection']
@@ -51,6 +51,10 @@ expectAssignable<RequiredCreateEncryptedCollectionSettings>({
 
 {
   // KMSProviders
+  // local
+  expectAssignable<KMSProviders['local']>({ key: '' });
+  expectAssignable<KMSProviders['local']>({ key: Buffer.alloc(0) });
+  expectAssignable<KMSProviders['local']>({ key: Binary.createFromBase64('') });
   // aws
   expectAssignable<KMSProviders['aws']>({ accessKeyId: '', secretAccessKey: '' });
   expectAssignable<KMSProviders['aws']>({