diff --git a/src/domain/session/room/timeline/ReactionsViewModel.js b/src/domain/session/room/timeline/ReactionsViewModel.js
index 25d74b49..c049dd11 100644
--- a/src/domain/session/room/timeline/ReactionsViewModel.js
+++ b/src/domain/session/room/timeline/ReactionsViewModel.js
@@ -188,7 +188,7 @@ import {NullLogItem, NullLogger} from "../../../../logging/NullLogger.js";
 import {HomeServer as MockHomeServer} from "../../../../mocks/HomeServer.js";
 // other imports
 import {BaseMessageTile} from "./tiles/BaseMessageTile.js";
-import {MappedList} from "../../../../observable/list/MappedList.js";
+import {MappedList} from "../../../../observable/list/MappedList";
 import {ObservableValue} from "../../../../observable/ObservableValue";
 import {PowerLevels} from "../../../../matrix/room/PowerLevels.js";
 
diff --git a/src/observable/index.js b/src/observable/index.js
index 9784444b..35ecaffc 100644
--- a/src/observable/index.js
+++ b/src/observable/index.js
@@ -22,7 +22,7 @@ import {BaseObservableMap} from "./map/BaseObservableMap.js";
 // re-export "root" (of chain) collections
 export { ObservableArray } from "./list/ObservableArray";
 export { SortedArray } from "./list/SortedArray.js";
-export { MappedList } from "./list/MappedList.js";
+export { MappedList } from "./list/MappedList";
 export { AsyncMappedList } from "./list/AsyncMappedList";
 export { ConcatList } from "./list/ConcatList";
 export { ObservableMap } from "./map/ObservableMap.js";
diff --git a/src/observable/list/MappedList.js b/src/observable/list/MappedList.ts
similarity index 100%
rename from src/observable/list/MappedList.js
rename to src/observable/list/MappedList.ts