diff --git a/src/matrix/storage/idb/query-target.js b/src/matrix/storage/idb/query-target.js
index fa5b99f5..7e848218 100644
--- a/src/matrix/storage/idb/query-target.js
+++ b/src/matrix/storage/idb/query-target.js
@@ -17,6 +17,10 @@ export default class QueryTarget {
         }
     }
 
+    supports(methodName) {
+        return this._target.supports(methodName);
+    }
+
     get(key) {
         return reqAsPromise(this._target.get(key));
     }
diff --git a/src/matrix/storage/idb/store.js b/src/matrix/storage/idb/store.js
index 58709573..1b4d3733 100644
--- a/src/matrix/storage/idb/store.js
+++ b/src/matrix/storage/idb/store.js
@@ -6,6 +6,10 @@ class QueryTargetWrapper {
     constructor(qt) {
         this._qt = qt;
     }
+
+    supports(methodName) {
+        return !!this._qt[methodName];
+    }
     
     openKeyCursor(...params) {
         try {
diff --git a/src/matrix/storage/idb/stores/PendingEventStore.js b/src/matrix/storage/idb/stores/PendingEventStore.js
index d73b649e..d413ec63 100644
--- a/src/matrix/storage/idb/stores/PendingEventStore.js
+++ b/src/matrix/storage/idb/stores/PendingEventStore.js
@@ -36,7 +36,13 @@ export default class PendingEventStore {
 
     async exists(roomId, queueIndex) {
         const keyRange = IDBKeyRange.only(encodeKey(roomId, queueIndex));
-        const key = await this._eventStore.getKey(keyRange);
+        let key;
+        if (this._eventStore.supports("getKey")) {
+            key = await this._eventStore.getKey(keyRange);
+        } else {
+            const value = await this._eventStore.get(keyRange);
+            key = value && value.key;
+        }
         return !!key;
     }