diff --git a/src/vs/vscode.d.ts b/src/vs/vscode.d.ts
index 778c36d53fbdfcce826a7614f022f0be5fcd0eb5..a1073d34724b2dd79b37229ada6e3bfb670f1ea7 100644
--- a/src/vs/vscode.d.ts
+++ b/src/vs/vscode.d.ts
@@ -5454,6 +5454,49 @@ declare module 'vscode' {
 		 */
 		export function asRelativePath(pathOrUri: string | Uri, includeWorkspaceFolder?: boolean): string;
 
+		/**
+		 * This method replaces `deleteCount` [workspace folders](#workspace.workspaceFolders) starting at index `start`
+		 * by an optional set of `workspaceFoldersToAdd` on the `vscode.workspace.workspaceFolders` array. This "splice"
+		 * behavior can be used to add, remove and change workspace folders in a single operation.
+		 *
+		 * If the first workspace folder is added, removed or changed, the currently executing extensions (including the
+		 * one that called this method) will be terminated and restarted so that the (deprecated) `rootPath` property is
+		 * updated to point to the first workspace folder.
+		 *
+		 * Use the [`onDidChangeWorkspaceFolders()`](#onDidChangeWorkspaceFolders) event to get notified when the
+		 * workspace folders have been updated.
+		 *
+		 * **Example:** adding a new workspace folder at the end of workspace folders
+		 * ```typescript
+		 * workspace.updateWorkspaceFolders(workspace.workspaceFolders ? workspace.workspaceFolders.length : 0, null, { uri: ...});
+		 * ```
+		 *
+		 * **Example:** removing the first workspace folder
+		 * ```typescript
+		 * workspace.updateWorkspaceFolders(0, 1);
+		 * ```
+		 *
+		 * **Example:** replacing an existing workspace folder with a new one
+		 * ```typescript
+		 * workspace.updateWorkspaceFolders(0, 1, { uri: ...});
+		 * ```
+		 *
+		 * It is valid to remove an existing workspace folder and add it again with a different name
+		 * to rename that folder.
+		 *
+		 * **Note:** it is not valid to call [updateWorkspaceFolders()](#updateWorkspaceFolders) multiple times
+		 * without waiting for the [`onDidChangeWorkspaceFolders()`](#onDidChangeWorkspaceFolders) to fire.
+		 *
+		 * @param start the zero-based location in the list of currently opened [workspace folders](#WorkspaceFolder)
+		 * from which to start deleting workspace folders.
+		 * @param deleteCount the optional number of workspace folders to remove.
+		 * @param workspaceFoldersToAdd the optional variable set of workspace folders to add in place of the deleted ones.
+		 * Each workspace is identified with a mandatory URI and an optional name.
+		 * @return true if the operation was successfully started and false otherwise if arguments were used that would result
+		 * in invalid workspace folder state (e.g. 2 folders with the same URI).
+		 */
+		export function updateWorkspaceFolders(start: number, deleteCount: number | undefined | null, ...workspaceFoldersToAdd: { uri: Uri, name?: string }[]): boolean;
+
 		/**
 		 * Creates a file system watcher.
 		 *
diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 5943dfa563adde76389c3fd0523bc41135e835ae..4f78dc021aa20d190625c2ca6ceaefeca796fb7d 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -214,49 +214,6 @@ declare module 'vscode' {
 
 	export namespace workspace {
 		export function registerFileSystemProvider(scheme: string, provider: FileSystemProvider): Disposable;
-
-		/**
-		 * This method replaces `deleteCount` [workspace folders](#workspace.workspaceFolders) starting at index `start`
-		 * by an optional set of `workspaceFoldersToAdd` on the `vscode.workspace.workspaceFolders` array. This "splice"
-		 * behavior can be used to add, remove and change workspace folders in a single operation.
-		 *
-		 * If the first workspace folder is added, removed or changed, the currently executing extensions (including the
-		 * one that called this method) will be terminated and restarted so that the (deprecated) `rootPath` property is
-		 * updated to point to the first workspace folder.
-		 *
-		 * Use the [`onDidChangeWorkspaceFolders()`](#onDidChangeWorkspaceFolders) event to get notified when the
-		 * workspace folders have been updated.
-		 *
-		 * **Example:** adding a new workspace folder at the end of workspace folders
-		 * ```typescript
-		 * workspace.updateWorkspaceFolders(workspace.workspaceFolders ? workspace.workspaceFolders.length : 0, null, { uri: ...});
-		 * ```
-		 *
-		 * **Example:** removing the first workspace folder
-		 * ```typescript
-		 * workspace.updateWorkspaceFolders(0, 1);
-		 * ```
-		 *
-		 * **Example:** replacing an existing workspace folder with a new one
-		 * ```typescript
-		 * workspace.updateWorkspaceFolders(0, 1, { uri: ...});
-		 * ```
-		 *
-		 * It is valid to remove an existing workspace folder and add it again with a different name
-		 * to rename that folder.
-		 *
-		 * **Note:** it is not valid to call [updateWorkspaceFolders()](#updateWorkspaceFolders) multiple times
-		 * without waiting for the [`onDidChangeWorkspaceFolders()`](#onDidChangeWorkspaceFolders) to fire.
-		 *
-		 * @param start the zero-based location in the list of currently opened [workspace folders](#WorkspaceFolder)
-		 * from which to start deleting workspace folders.
-		 * @param deleteCount the optional number of workspace folders to remove.
-		 * @param workspaceFoldersToAdd the optional variable set of workspace folders to add in place of the deleted ones.
-		 * Each workspace is identified with a mandatory URI and an optional name.
-		 * @return true if the operation was successfully started and false otherwise if arguments were used that would result
-		 * in invalid workspace folder state (e.g. 2 folders with the same URI).
-		 */
-		export function updateWorkspaceFolders(start: number, deleteCount: number, ...workspaceFoldersToAdd: { uri: Uri, name?: string }[]): boolean;
 	}
 
 	export namespace window {
diff --git a/src/vs/workbench/api/node/extHost.api.impl.ts b/src/vs/workbench/api/node/extHost.api.impl.ts
index eac6bb4ffe7794e9c80f3d8bd4b19761b8300cae..e4bf9f86263949933e10f874041d466dc31afaae 100644
--- a/src/vs/workbench/api/node/extHost.api.impl.ts
+++ b/src/vs/workbench/api/node/extHost.api.impl.ts
@@ -433,9 +433,9 @@ export function createApiFactory(
 			set name(value) {
 				throw errors.readonly();
 			},
-			updateWorkspaceFolders: proposedApiFunction(extension, (index, deleteCount, ...workspaceFoldersToAdd) => {
-				return extHostWorkspace.updateWorkspaceFolders(extension, index, deleteCount, ...workspaceFoldersToAdd);
-			}),
+			updateWorkspaceFolders: (index, deleteCount, ...workspaceFoldersToAdd) => {
+				return extHostWorkspace.updateWorkspaceFolders(extension, index, deleteCount || 0, ...workspaceFoldersToAdd);
+			},
 			onDidChangeWorkspaceFolders: function (listener, thisArgs?, disposables?) {
 				return extHostWorkspace.onDidChangeWorkspace(listener, thisArgs, disposables);
 			},