diff --git a/src/Buffer.spec.ts b/src/Buffer.spec.ts
index c8a31061..132e0152 100644
--- a/src/Buffer.spec.ts
+++ b/src/Buffer.spec.ts
@@ -75,7 +75,7 @@ describe('Buffer', () => {
   });
 
   it('constructs from an iterable', () => {
-    const q = Buffer.from([1, 2, 3], 2);
+    const q: Iterable<number> = Buffer.from([1, 2, 3], 2);
     expect([...q]).toEqual([2, 3]);
   });
 
diff --git a/src/Buffer.ts b/src/Buffer.ts
index 9364a7db..42bd4178 100644
--- a/src/Buffer.ts
+++ b/src/Buffer.ts
@@ -61,10 +61,11 @@ export default class Buffer<A> {
         return this.length > 0
           ? {
               value: this.dequeue(),
-              done: false,
+              done: false as const,
             }
           : {
-              done: true,
+              done: true as const,
+              value: undefined,
             };
       },
       [Symbol.iterator]() {