diff --git a/lib/modules/firestore/DocumentReference.js b/lib/modules/firestore/DocumentReference.js
index 1e77823a..946e6d39 100644
--- a/lib/modules/firestore/DocumentReference.js
+++ b/lib/modules/firestore/DocumentReference.js
@@ -112,7 +112,7 @@ export default class DocumentReference {
         } else {
           throw new Error('DocumentReference.onSnapshot failed: Observer.next must be a valid function.');
         }
-      } else if (optionsOrObserverOrOnNext.includeMetadataChanges) {
+      } else if (Object.prototype.hasOwnProperty.call(optionsOrObserverOrOnNext, 'includeMetadataChanges')) {
         docListenOptions = optionsOrObserverOrOnNext;
         // Called with: Options, onNext, ?onError
         if (isFunction(observerOrOnNextOrOnError)) {
diff --git a/lib/modules/firestore/Query.js b/lib/modules/firestore/Query.js
index cc4190e0..006b2c18 100644
--- a/lib/modules/firestore/Query.js
+++ b/lib/modules/firestore/Query.js
@@ -201,7 +201,8 @@ export default class Query {
         } else {
           throw new Error('Query.onSnapshot failed: Observer.next must be a valid function.');
         }
-      } else if (optionsOrObserverOrOnNext.includeDocumentMetadataChanges || optionsOrObserverOrOnNext.includeQueryMetadataChanges) {
+      } else if (Object.prototype.hasOwnProperty.call(optionsOrObserverOrOnNext, 'includeDocumentMetadataChanges')
+        || Object.prototype.hasOwnProperty.call(optionsOrObserverOrOnNext, 'includeQueryMetadataChanges')) {
         queryListenOptions = optionsOrObserverOrOnNext;
         // Called with: Options, onNext, ?onError
         if (isFunction(observerOrOnNextOrOnError)) {