diff --git a/.changeset/few-snails-walk.md b/.changeset/few-snails-walk.md
new file mode 100644
index 00000000000..a845151cc84
--- /dev/null
+++ b/.changeset/few-snails-walk.md
@@ -0,0 +1,2 @@
+---
+---
diff --git a/packages/firestore/exp/index.node.ts b/packages/firestore/exp/index.node.ts
index 5113219901e..1b7d4774d4c 100644
--- a/packages/firestore/exp/index.node.ts
+++ b/packages/firestore/exp/index.node.ts
@@ -54,6 +54,7 @@ export {
   getDocFromCache,
   getDocFromServer,
   onSnapshot,
+  onSnapshotsInSync,
   setDoc,
   updateDoc,
   deleteDoc,
diff --git a/packages/firestore/exp/src/api/reference.ts b/packages/firestore/exp/src/api/reference.ts
index bbc30bd0449..3f1bcdea6b0 100644
--- a/packages/firestore/exp/src/api/reference.ts
+++ b/packages/firestore/exp/src/api/reference.ts
@@ -29,6 +29,7 @@ import { cast } from '../../../lite/src/api/util';
 import { DocumentSnapshot, QuerySnapshot } from './snapshot';
 import {
   addDocSnapshotListener,
+  addSnapshotsInSyncListener,
   addQuerySnapshotListener,
   applyFirestoreDataConverter,
   getDocsViaSnapshotListener,
@@ -431,6 +432,45 @@ export function onSnapshot<T>(
   };
 }
 
+// TODO(firestorexp): Make sure these overloads are tested via the Firestore
+// integration tests
+export function onSnapshotsInSync(
+  firestore: firestore.FirebaseFirestore,
+  observer: {
+    next?: (value: void) => void;
+    error?: (error: firestore.FirestoreError) => void;
+    complete?: () => void;
+  }
+): Unsubscribe;
+export function onSnapshotsInSync(
+  firestore: firestore.FirebaseFirestore,
+  onSync: () => void
+): Unsubscribe;
+export function onSnapshotsInSync(
+  firestore: firestore.FirebaseFirestore,
+  arg: unknown
+): Unsubscribe {
+  const firestoreImpl = cast(firestore, Firestore);
+  const observer = isPartialObserver(arg)
+    ? (arg as PartialObserver<void>)
+    : {
+        next: arg as () => void
+      };
+
+  const asyncObserver = firestoreImpl
+    ._getFirestoreClient()
+    .then(firestoreClient =>
+      addSnapshotsInSyncListener(firestoreClient, observer)
+    );
+
+  // TODO(firestorexp): Add test that verifies that we don't raise a snapshot if
+  // unsubscribe is called before `asyncObserver` resolves.
+  return () => {
+    // eslint-disable-next-line @typescript-eslint/no-floating-promises
+    asyncObserver.then(unsubscribe => unsubscribe());
+  };
+}
+
 /**
  * Converts a ViewSnapshot that contains the single document specified by `ref`
  * to a DocumentSnapshot.
diff --git a/packages/firestore/src/api/database.ts b/packages/firestore/src/api/database.ts
index 47cab0ec39e..9625ac3086c 100644
--- a/packages/firestore/src/api/database.ts
+++ b/packages/firestore/src/api/database.ts
@@ -462,37 +462,19 @@ export class Firestore implements firestore.FirebaseFirestore, FirebaseService {
     this.ensureClientConfigured();
 
     if (isPartialObserver(arg)) {
-      return this.onSnapshotsInSyncInternal(arg as PartialObserver<void>);
+      return addSnapshotsInSyncListener(
+        this._firestoreClient!,
+        arg as PartialObserver<void>
+      );
     } else {
       validateArgType('Firestore.onSnapshotsInSync', 'function', 1, arg);
       const observer: PartialObserver<void> = {
         next: arg as () => void
       };
-      return this.onSnapshotsInSyncInternal(observer);
+      return addSnapshotsInSyncListener(this._firestoreClient!, observer);
     }
   }
 
-  private onSnapshotsInSyncInternal(
-    observer: PartialObserver<void>
-  ): Unsubscribe {
-    const errHandler = (err: Error): void => {
-      throw fail('Uncaught Error in onSnapshotsInSync');
-    };
-    const asyncObserver = new AsyncObserver<void>({
-      next: () => {
-        if (observer.next) {
-          observer.next();
-        }
-      },
-      error: errHandler
-    });
-    this._firestoreClient!.addSnapshotsInSyncListener(asyncObserver);
-    return () => {
-      asyncObserver.mute();
-      this._firestoreClient!.removeSnapshotsInSyncListener(asyncObserver);
-    };
-  }
-
   ensureClientConfigured(): FirestoreClient {
     if (!this._firestoreClient) {
       // Kick off starting the client but don't actually wait for it.
@@ -675,6 +657,29 @@ export class Firestore implements firestore.FirebaseFirestore, FirebaseService {
   }
 }
 
+/** Registers the listener for onSnapshotsInSync() */
+export function addSnapshotsInSyncListener(
+  firestoreClient: FirestoreClient,
+  observer: PartialObserver<void>
+): Unsubscribe {
+  const errHandler = (err: Error): void => {
+    throw fail('Uncaught Error in onSnapshotsInSync');
+  };
+  const asyncObserver = new AsyncObserver<void>({
+    next: () => {
+      if (observer.next) {
+        observer.next();
+      }
+    },
+    error: errHandler
+  });
+  firestoreClient.addSnapshotsInSyncListener(asyncObserver);
+  return () => {
+    asyncObserver.mute();
+    firestoreClient.removeSnapshotsInSyncListener(asyncObserver);
+  };
+}
+
 /**
  * A reference to a transaction.
  */