diff --git a/src/matrix/e2ee/megolm/decryption/KeyLoader.ts b/src/matrix/e2ee/megolm/decryption/KeyLoader.ts
index c1925e84..884203a3 100644
--- a/src/matrix/e2ee/megolm/decryption/KeyLoader.ts
+++ b/src/matrix/e2ee/megolm/decryption/KeyLoader.ts
@@ -213,6 +213,9 @@ class KeyOperation {
     }
 }
 
+import {KeySource} from "../../../storage/idb/stores/InboundGroupSessionStore";
+
+
 export function tests() {
     let instances = 0;
 
@@ -237,6 +240,8 @@ export function tests() {
         get serializationKey(): string { return `key-${this.sessionId}-${this._firstKnownIndex}`; }
         get serializationType(): string { return "type"; }
         get eventIds(): string[] | undefined { return undefined; }
+        get keySource(): KeySource { return KeySource.DeviceMessage; }
+
         loadInto(session: Olm.InboundGroupSession) {
             const mockSession = session as MockInboundSession;
             mockSession.sessionId = this.sessionId;
diff --git a/src/matrix/e2ee/megolm/decryption/RoomKey.ts b/src/matrix/e2ee/megolm/decryption/RoomKey.ts
index 6112ccef..7b648d92 100644
--- a/src/matrix/e2ee/megolm/decryption/RoomKey.ts
+++ b/src/matrix/e2ee/megolm/decryption/RoomKey.ts
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import {BackupStatus} from "../../../storage/idb/stores/InboundGroupSessionStore";
+import {BackupStatus, KeySource} from "../../../storage/idb/stores/InboundGroupSessionStore";
 import type {InboundGroupSessionEntry} from "../../../storage/idb/stores/InboundGroupSessionStore";
 import type {Transaction} from "../../../storage/idb/Transaction";
 import type {DecryptionResult} from "../../DecryptionResult";
@@ -83,6 +83,7 @@ export abstract class IncomingRoomKey extends RoomKey {
             sessionId: this.sessionId,
             session: pickledSession,
             backup: this.backupStatus,
+            source: this.keySource,
             claimedKeys: {"ed25519": this.claimedEd25519Key},
         };
         txn.inboundGroupSessions.set(sessionEntry);
@@ -131,6 +132,8 @@ export abstract class IncomingRoomKey extends RoomKey {
     protected get backupStatus(): BackupStatus {
         return BackupStatus.NotBackedUp;
     }
+
+    protected abstract get keySource(): KeySource;
 }
 
 class DeviceMessageRoomKey extends IncomingRoomKey {
@@ -147,10 +150,12 @@ class DeviceMessageRoomKey extends IncomingRoomKey {
     get claimedEd25519Key() { return this._decryptionResult.claimedEd25519Key; }
     get serializationKey(): string { return this._decryptionResult.event.content?.["session_key"]; }
     get serializationType(): string { return "create"; }
+    protected get keySource(): KeySource { return KeySource.DeviceMessage; }
 
     loadInto(session) {
         session.create(this.serializationKey);
     }
+
 }
 
 class BackupRoomKey extends IncomingRoomKey {
@@ -164,7 +169,8 @@ class BackupRoomKey extends IncomingRoomKey {
     get claimedEd25519Key() { return this._backupInfo["sender_claimed_keys"]?.["ed25519"]; }
     get serializationKey(): string { return this._backupInfo["session_key"]; }
     get serializationType(): string { return "import_session"; }
-    
+    protected get keySource(): KeySource { return KeySource.Backup; }
+
     loadInto(session) {
         session.import_session(this.serializationKey);
     }
diff --git a/src/matrix/storage/idb/schema.ts b/src/matrix/storage/idb/schema.ts
index e6644fd0..9c105a71 100644
--- a/src/matrix/storage/idb/schema.ts
+++ b/src/matrix/storage/idb/schema.ts
@@ -6,7 +6,7 @@ import {addRoomToIdentity} from "../../e2ee/DeviceTracker.js";
 import {SESSION_E2EE_KEY_PREFIX} from "../../e2ee/common.js";
 import {SummaryData} from "../../room/RoomSummary";
 import {RoomMemberStore, MemberData} from "./stores/RoomMemberStore";
-import {InboundGroupSessionStore, InboundGroupSessionEntry, BackupStatus} from "./stores/InboundGroupSessionStore";
+import {InboundGroupSessionStore, InboundGroupSessionEntry, BackupStatus, KeySource} from "./stores/InboundGroupSessionStore";
 import {RoomStateEntry} from "./stores/RoomStateStore";
 import {SessionStore} from "./stores/SessionStore";
 import {Store} from "./Store";
@@ -283,6 +283,11 @@ async function addInboundSessionBackupIndex(db: IDBDatabase, txn: IDBTransaction
     const inboundGroupSessions = txn.objectStore("inboundGroupSessions");
     await iterateCursor<InboundGroupSessionEntry>(inboundGroupSessions.openCursor(), (value, key, cursor) => {
         value.backup = BackupStatus.NotBackedUp;
+        // we'll also have backup keys in here, we can't tell,
+        // but the worst thing that can happen is that we try
+        // to backup keys that were already in backup, which
+        // the server will ignore
+        value.source = KeySource.DeviceMessage;
         return NOT_DONE;
     });
     inboundGroupSessions.createIndex("byBackup", "backup", {unique: false});
diff --git a/src/matrix/storage/idb/stores/InboundGroupSessionStore.ts b/src/matrix/storage/idb/stores/InboundGroupSessionStore.ts
index 72ea6e9a..96b127f7 100644
--- a/src/matrix/storage/idb/stores/InboundGroupSessionStore.ts
+++ b/src/matrix/storage/idb/stores/InboundGroupSessionStore.ts
@@ -22,6 +22,11 @@ export enum BackupStatus {
     BackedUp = 1
 }
 
+export enum KeySource {
+    DeviceMessage = 1,
+    Backup,
+}
+
 export interface InboundGroupSessionEntry {
     roomId: string;
     senderKey: string;
@@ -29,7 +34,8 @@ export interface InboundGroupSessionEntry {
     session?: string;
     claimedKeys?: { [algorithm : string] : string };
     eventIds?: string[];
-    backup: BackupStatus
+    backup: BackupStatus,
+    source: KeySource
 }
 
 type InboundGroupSessionStorageEntry = InboundGroupSessionEntry & { key: string };