diff --git a/types/google-cloud__storage/google-cloud__storage-tests.ts b/types/google-cloud__storage/google-cloud__storage-tests.ts
index e701fe5681..a301aa063c 100644
--- a/types/google-cloud__storage/google-cloud__storage-tests.ts
+++ b/types/google-cloud__storage/google-cloud__storage-tests.ts
@@ -38,7 +38,7 @@ export class TestStorage {
   };
 
   // import Storage class
-  static gcs: Storage;
+  static gcs: Storage = new Storage();
 
   // the bucket
   private buckets: Bucket[] = [];
diff --git a/types/google-cloud__storage/index.d.ts b/types/google-cloud__storage/index.d.ts
index eaf1177950..c87a2cc606 100644
--- a/types/google-cloud__storage/index.d.ts
+++ b/types/google-cloud__storage/index.d.ts
@@ -313,7 +313,7 @@ declare module "@google-cloud/storage/storage" {
     keyFilename?: string;
     maxRetries?: number;
     projectId?: string;
-    promise?: Function;
+    promise?: PromiseLibrary<any>;
   }
 
   /**
@@ -366,4 +366,6 @@ declare module "@google-cloud/storage/storage" {
     getBuckets(query?: BucketQuery): Promise<[Bucket[]]>;
     getBucketsStream(query?: BucketQuery): Promise<[ReadStream]>;
   }
+
+  type PromiseLibrary<T> = () => PromiseLike<T>;
 }