diff --git a/src/vs/workbench/api/common/extHostTreeViews.ts b/src/vs/workbench/api/common/extHostTreeViews.ts
index f5e63bdc8cc0c..86ac1db54eaa9 100644
--- a/src/vs/workbench/api/common/extHostTreeViews.ts
+++ b/src/vs/workbench/api/common/extHostTreeViews.ts
@@ -139,12 +139,11 @@ export class ExtHostTreeViews implements ExtHostTreeViewsShape {
 		if ((sourceViewId === destinationViewId) && sourceTreeItemHandles) {
 			const additionalTransferItems = await treeView.onWillDrop(sourceTreeItemHandles);
 			if (additionalTransferItems) {
-				for (const key of additionalTransferItems.items.keys()) {
-					const item = additionalTransferItems.items.get(key);
-					if (item) {
-						treeDataTransfer.items.set(key, item);
+				additionalTransferItems.items.forEach((value, key) => {
+					if (value) {
+						treeDataTransfer.items.set(key, value);
 					}
-				}
+				});
 			}
 		}
 		return treeView.onDrop(treeDataTransfer, newParentItemHandle);
diff --git a/src/vscode-dts/vscode.proposed.treeViewDragAndDrop.d.ts b/src/vscode-dts/vscode.proposed.treeViewDragAndDrop.d.ts
index b2ae05a46a2a1..293666e129624 100644
--- a/src/vscode-dts/vscode.proposed.treeViewDragAndDrop.d.ts
+++ b/src/vscode-dts/vscode.proposed.treeViewDragAndDrop.d.ts
@@ -38,7 +38,7 @@ declare module 'vscode' {
 		 */
 		items: {
 			get: (mimeType: string) => TreeDataTransferItem | undefined
-			keys: () => IterableIterator<string>;
+			forEach: (callbackfn: (value: TreeDataTransferItem, key: string) => void) => void;
 		};
 	}