diff --git a/packages/firestore/CHANGELOG.md b/packages/firestore/CHANGELOG.md
index 6c210345e54..7281ff0d962 100644
--- a/packages/firestore/CHANGELOG.md
+++ b/packages/firestore/CHANGELOG.md
@@ -1,4 +1,8 @@
 # Unreleased
+- [fixed] Fixed an issue where `CollectionReference.add()` would reject
+  custom types when using `withConverter()`. (#2606)
+
+# 1.9.3
 - [fixed] Fixed an issue where auth credentials were not respected in some
   Firefox or Chrome extensions. (#1491)
 - [changed] Firestore previously required that every document read in a
diff --git a/packages/firestore/src/api/database.ts b/packages/firestore/src/api/database.ts
index 99575a675ad..6fc11907499 100644
--- a/packages/firestore/src/api/database.ts
+++ b/packages/firestore/src/api/database.ts
@@ -2461,7 +2461,10 @@ export class CollectionReference<T = firestore.DocumentData> extends Query<T>
 
   add(value: T): Promise<firestore.DocumentReference<T>> {
     validateExactNumberOfArgs('CollectionReference.add', arguments, 1);
-    validateArgType('CollectionReference.add', 'object', 1, value);
+    const convertedValue = this._converter
+      ? this._converter.toFirestore(value)
+      : value;
+    validateArgType('CollectionReference.add', 'object', 1, convertedValue);
     const docRef = this.doc();
     return docRef.set(value).then(() => docRef);
   }
diff --git a/packages/firestore/test/integration/api/database.test.ts b/packages/firestore/test/integration/api/database.test.ts
index 763201959ee..7213a3dd766 100644
--- a/packages/firestore/test/integration/api/database.test.ts
+++ b/packages/firestore/test/integration/api/database.test.ts
@@ -1214,12 +1214,9 @@ apiDescribe('Database', (persistence: boolean) => {
 
     it('for CollectionReference.withConverter()', () => {
       return withTestDb(persistence, async db => {
-        const docRef = db
-          .collection('posts')
-          .withConverter(postConverter)
-          .doc();
+        const coll = db.collection('posts').withConverter(postConverter);
 
-        await docRef.set(new Post('post', 'author'));
+        const docRef = await coll.add(new Post('post', 'author'));
         const postData = await docRef.get();
         const post = postData.data();
         expect(post).to.not.equal(undefined);