diff --git a/src/vs/workbench/api/common/extHost.protocol.ts b/src/vs/workbench/api/common/extHost.protocol.ts
index 94630f2404a..86d8dde204b 100644
--- a/src/vs/workbench/api/common/extHost.protocol.ts
+++ b/src/vs/workbench/api/common/extHost.protocol.ts
@@ -257,7 +257,7 @@ export interface MainThreadTextEditorsShape extends IDisposable {
 }
 
 export interface MainThreadTreeViewsShape extends IDisposable {
-	$registerTreeViewDataProvider(treeViewId: string, options: { showCollapseAll: boolean; canSelectMany: boolean; dropMimeTypes: string[]; dragMimeTypes: string[]; hasHandleDrag: boolean; hasHandleDrop: boolean }): Promise<void>;
+	$registerTreeViewDataProvider(treeViewId: string, options: { showCollapseAll: boolean; canSelectMany: boolean; dropMimeTypes: readonly string[]; dragMimeTypes: readonly string[]; hasHandleDrag: boolean; hasHandleDrop: boolean }): Promise<void>;
 	$refresh(treeViewId: string, itemsToRefresh?: { [treeItemHandle: string]: ITreeItem }): Promise<void>;
 	$reveal(treeViewId: string, itemInfo: { item: ITreeItem; parentChain: ITreeItem[] } | undefined, options: IRevealOptions): Promise<void>;
 	$setMessage(treeViewId: string, message: string): void;
diff --git a/src/vscode-dts/vscode.d.ts b/src/vscode-dts/vscode.d.ts
index ba8a277adad..badebabb873 100644
--- a/src/vscode-dts/vscode.d.ts
+++ b/src/vscode-dts/vscode.d.ts
@@ -9830,7 +9830,7 @@ declare module 'vscode' {
 		 *
 		 * Note that mime types that cannot be sent to the extension will be omitted.
 		 */
-		readonly dropMimeTypes: string[];
+		readonly dropMimeTypes: readonly string[];
 
 		/**
 		 * The mime types that the {@link TreeDragAndDropController.handleDrag `handleDrag`} method of this `TreeDragAndDropController` may add to the tree data transfer.
@@ -9838,7 +9838,7 @@ declare module 'vscode' {
 		 *
 		 * The recommended mime type of the tree (`application/vnd.code.tree.<treeidlowercase>`) will be automatically added.
 		 */
-		readonly dragMimeTypes: string[];
+		readonly dragMimeTypes: readonly string[];
 
 		/**
 		 * When the user starts dragging items from this `DragAndDropController`, `handleDrag` will be called.
@@ -9856,7 +9856,7 @@ declare module 'vscode' {
 		 * @param dataTransfer The data transfer associated with this drag.
 		 * @param token A cancellation token indicating that drag has been cancelled.
 		 */
-		handleDrag?(source: T[], dataTransfer: DataTransfer, token: CancellationToken): Thenable<void> | void;
+		handleDrag?(source: readonly T[], dataTransfer: DataTransfer, token: CancellationToken): Thenable<void> | void;
 
 		/**
 		 * Called when a drag and drop action results in a drop on the tree that this `DragAndDropController` belongs to.