diff --git a/src/Future.ts b/src/Future.ts
index 3b4af3c..1c61386 100644
--- a/src/Future.ts
+++ b/src/Future.ts
@@ -269,7 +269,7 @@ export class Future<T> {
      * This method is eager, will trigger the underlying Promise.
      */
     mapFailure(fn: (x:any)=>any): Future<T> {
-        const lazy = Lazy.of(()=>this.promise.get().catch(x => {throw [fn(x)]}));
+        const lazy = Lazy.of(()=>this.promise.get().catch(x => {throw fn(x)}));
         lazy.get();
         return new Future<T>(lazy);
     }
diff --git a/tests/Future.ts b/tests/Future.ts
index 6a2d50a..60a8dcf 100644
--- a/tests/Future.ts
+++ b/tests/Future.ts
@@ -9,7 +9,7 @@ async function ensureFailedWithValue<T>(val: any, promise:Promise<T>) {
         v = await promise;
         assert.ok(false);
     } catch (err) {
-        assert.equal(val, err);
+        assert.deepEqual(val, err);
     }
 }
 
@@ -96,7 +96,7 @@ describe("Future.map*", () => {
     });
     it("mapFailure works", async () => {
         return ensureFailedWithValue(
-            "oops, sorry", Future.failed("sorry").mapFailure(err => "oops, " + err).toPromise());
+            "SORRY", Future.failed("sorry").mapFailure(err => err.toUpperCase()).toPromise());
     });
     it("mapFailure is a nop on successful futures", async () => {
         assert.deepEqual(5, await Future.ok(5).mapFailure(_ => "oops"));