diff --git a/src/matrix/e2ee/megolm/decryption/KeyLoader.ts b/src/matrix/e2ee/megolm/decryption/KeyLoader.ts
index 1618a4a6..375fb2ac 100644
--- a/src/matrix/e2ee/megolm/decryption/KeyLoader.ts
+++ b/src/matrix/e2ee/megolm/decryption/KeyLoader.ts
@@ -156,7 +156,7 @@ export class KeyLoader extends BaseLRUCache<KeyOperation> {
 
     private findIndexSameKey(key: IRoomKey): number {
         return this._entries.findIndex(op => {
-            return op.isForKey(key);
+            return op.isForSameSession(key.roomId, key.senderKey, key.sessionId) && op.isForKey(key);
         });
     }
 
@@ -213,7 +213,6 @@ class KeyOperation {
 
 export function tests() {
     let instances = 0;
-    let idCounter = 0;
 
     class MockRoomKey implements IRoomKey {
         private _roomId: string;
@@ -232,7 +231,7 @@ export function tests() {
         get senderKey(): string { return this._senderKey; }
         get sessionId(): string { return this._sessionId; }
         get claimedEd25519Key(): string { return "claimedEd25519Key"; }
-        get serializationKey(): string { return "key"; }
+        get serializationKey(): string { return `key-${this.sessionId}-${this._firstKnownIndex}`; }
         get serializationType(): string { return "type"; }
         get eventIds(): string[] | undefined { return undefined; }
         loadInto(session: OlmInboundGroupSession) {
@@ -246,6 +245,10 @@ export function tests() {
         public sessionId: string = "";
         public firstKnownIndex: number = 0;
 
+        constructor() {
+            instances += 1;
+        }
+
         free(): void { instances -= 1; }
         pickle(key: string | Uint8Array): string { return `${this.sessionId}-pickled-session`; }
         unpickle(key: string | Uint8Array, pickle: string) {}
@@ -262,18 +265,109 @@ export function tests() {
     const roomId = "!abc:hs.tld";
     const aliceSenderKey = "abc";
     const bobSenderKey = "def";
-    const sessionId = "s123";
+    const sessionId1 = "s123";
+    const sessionId2 = "s456";
+    const sessionId3 = "s789";
     
     return {
         "load key gives correct session": async assert => {
-            const loader = new KeyLoader(olm, PICKLE_KEY, 5);
+            const loader = new KeyLoader(olm, PICKLE_KEY, 2);
+            let callback1Called = false;
+            let callback2Called = false;
+            const p1 = loader.useKey(new MockRoomKey(roomId, aliceSenderKey, sessionId1, 1), async session => {
+                callback1Called = true;
+                assert.equal(session.session_id(), sessionId1);
+                assert.equal(session.first_known_index(), 1);
+                await Promise.resolve(); // make sure they are busy in parallel
+            });
+            const p2 = loader.useKey(new MockRoomKey(roomId, aliceSenderKey, sessionId2, 2), async session => {
+                callback2Called = true;
+                assert.equal(session.session_id(), sessionId2);
+                assert.equal(session.first_known_index(), 2);
+                await Promise.resolve(); // make sure they are busy in parallel
+            });
+            assert.equal(loader.size, 2);
+            await Promise.all([p1, p2]);
+            assert(callback1Called);
+            assert(callback2Called);
+        },
+        "keys with different first index are kept separate": async assert => {
+            const loader = new KeyLoader(olm, PICKLE_KEY, 2);
+            let callback1Called = false;
+            let callback2Called = false;
+            const p1 = loader.useKey(new MockRoomKey(roomId, aliceSenderKey, sessionId1, 1), async session => {
+                callback1Called = true;
+                assert.equal(session.session_id(), sessionId1);
+                assert.equal(session.first_known_index(), 1);
+                await Promise.resolve(); // make sure they are busy in parallel
+            });
+            const p2 = loader.useKey(new MockRoomKey(roomId, aliceSenderKey, sessionId1, 2), async session => {
+                callback2Called = true;
+                assert.equal(session.session_id(), sessionId1);
+                assert.equal(session.first_known_index(), 2);
+                await Promise.resolve(); // make sure they are busy in parallel
+            });
+            assert.equal(loader.size, 2);
+            await Promise.all([p1, p2]);
+            assert(callback1Called);
+            assert(callback2Called);
+        },
+        "useKey blocks as long as no free sessions are available": async assert => {
+            const loader = new KeyLoader(olm, PICKLE_KEY, 1);
+            let resolve;
             let callbackCalled = false;
-            await loader.useKey(new MockRoomKey(roomId, aliceSenderKey, sessionId, 1), session => {
+            loader.useKey(new MockRoomKey(roomId, aliceSenderKey, sessionId1, 1), async session => {
+                await new Promise(r => resolve = r);
+            });
+            await Promise.resolve();
+            assert.equal(loader.size, 1);
+            const promise = loader.useKey(new MockRoomKey(roomId, aliceSenderKey, sessionId2, 1), session => {
                 callbackCalled = true;
-                assert.equal(session.session_id(), sessionId);
+            });
+            assert.equal(callbackCalled, false);
+            resolve();
+            await promise;
+            assert.equal(callbackCalled, true);
+        },
+        "cache hit while key in use, then replace (check refCount works properly)": async assert => {
+            const loader = new KeyLoader(olm, PICKLE_KEY, 1);
+            let resolve1, resolve2;
+            const key1 = new MockRoomKey(roomId, aliceSenderKey, sessionId1, 1);
+            const p1 = loader.useKey(key1, async session => {
+                await new Promise(r => resolve1 = r);
+            });
+            const p2 = loader.useKey(key1, async session => {
+                await new Promise(r => resolve2 = r);
+            });
+            await Promise.resolve();
+            assert.equal(loader.size, 1);
+            assert.equal(loader.running, true);
+            resolve1();
+            await p1;
+            assert.equal(loader.running, true);
+            resolve2();
+            await p2;
+            assert.equal(loader.running, false);
+            let callbackCalled = false;
+            await loader.useKey(new MockRoomKey(roomId, aliceSenderKey, sessionId2, 1), async session => {
+                callbackCalled = true;
+                assert.equal(session.session_id(), sessionId2);
                 assert.equal(session.first_known_index(), 1);
             });
-            assert(callbackCalled);
+            assert.equal(loader.size, 1);
+            assert.equal(callbackCalled, true);
         },
+        "cache hit while key not in use": async assert => {
+            const loader = new KeyLoader(olm, PICKLE_KEY, 2);
+            let resolve1, resolve2, invocations = 0;
+            const key1 = new MockRoomKey(roomId, aliceSenderKey, sessionId1, 1);
+            await loader.useKey(key1, async session => { invocations += 1; });
+            assert.equal(loader.size, 1);
+            const cachedKey = loader.getCachedKey(roomId, aliceSenderKey, sessionId1)!;
+            assert.equal(cachedKey, key1);
+            await loader.useKey(cachedKey, async session => { invocations += 1; });
+            assert.equal(loader.size, 1);
+            assert.equal(invocations, 2);
+        }
     }
 }