diff --git a/src/deep-map-keys.ts b/src/deep-map-keys.ts
index 7148b87..a149803 100644
--- a/src/deep-map-keys.ts
+++ b/src/deep-map-keys.ts
@@ -55,7 +55,7 @@ export class DeepMapKeys {
     this.cache.set(obj, result);
 
     for (let key in obj) {
-      if (obj.hasOwnProperty(key)) {
+      if (Object.hasOwnProperty.call(obj, key)) {
         result[mapFn.call(thisArg, key, obj[key])] = this.map(obj[key]);
       }
     }
diff --git a/src/index.test.ts b/src/index.test.ts
index d6ba49b..7135cc5 100644
--- a/src/index.test.ts
+++ b/src/index.test.ts
@@ -102,3 +102,12 @@ describe('deepMapKeys(object, mapFn, [options])', () => {
   });
 
 });
+
+it('handles null prototype objects', () => {
+  const caps = (key: string) => key.toUpperCase(); 
+
+  const nullProtoObj = Object.create(null);
+  nullProtoObj.foo = 'bar';
+
+  deepMapKeys(nullProtoObj, caps).should.deep.equal({ FOO: 'bar' });
+});