diff --git a/src/vs/workbench/api/browser/mainThreadCustomEditors.ts b/src/vs/workbench/api/browser/mainThreadCustomEditors.ts
index 9bd40eeb40d..420344cb4b8 100644
--- a/src/vs/workbench/api/browser/mainThreadCustomEditors.ts
+++ b/src/vs/workbench/api/browser/mainThreadCustomEditors.ts
@@ -29,10 +29,12 @@ import { CustomDocumentBackupData } from 'vs/workbench/contrib/customEditor/brow
 import { ICustomEditorModel, ICustomEditorService } from 'vs/workbench/contrib/customEditor/common/customEditor';
 import { CustomTextEditorModel } from 'vs/workbench/contrib/customEditor/common/customTextEditorModel';
 import { WebviewExtensionDescription } from 'vs/workbench/contrib/webview/browser/webview';
+import { WebviewInput } from 'vs/workbench/contrib/webview/browser/webviewEditorInput';
 import { IWebviewWorkbenchService } from 'vs/workbench/contrib/webview/browser/webviewWorkbenchService';
 import { IBackupFileService } from 'vs/workbench/services/backup/common/backup';
 import { IEditorGroupsService } from 'vs/workbench/services/editor/common/editorGroupsService';
 import { IWorkbenchEnvironmentService } from 'vs/workbench/services/environment/common/environmentService';
+import { IExtensionService } from 'vs/workbench/services/extensions/common/extensions';
 import { IWorkingCopyFileService } from 'vs/workbench/services/workingCopy/common/workingCopyFileService';
 import { IWorkingCopy, IWorkingCopyBackup, IWorkingCopyService, WorkingCopyCapabilities } from 'vs/workbench/services/workingCopy/common/workingCopyService';
 
@@ -51,6 +53,7 @@ export class MainThreadCustomEditors extends Disposable implements extHostProtoc
 		private readonly mainThreadWebview: MainThreadWebviews,
 		private readonly mainThreadWebviewPanels: MainThreadWebviewPanels,
 		context: extHostProtocol.IExtHostContext,
+		@IExtensionService extensionService: IExtensionService,
 		@IWorkingCopyService workingCopyService: IWorkingCopyService,
 		@IWorkingCopyFileService workingCopyFileService: IWorkingCopyFileService,
 		@ICustomEditorService private readonly _customEditorService: ICustomEditorService,
@@ -63,7 +66,7 @@ export class MainThreadCustomEditors extends Disposable implements extHostProtoc
 
 		this._proxyCustomEditors = context.getProxy(extHostProtocol.ExtHostContext.ExtHostCustomEditors);
 
-		workingCopyFileService.registerWorkingCopyProvider((editorResource) => {
+		this._register(workingCopyFileService.registerWorkingCopyProvider((editorResource) => {
 			const matchedWorkingCopies: IWorkingCopy[] = [];
 
 			for (const workingCopy of workingCopyService.workingCopies) {
@@ -74,7 +77,18 @@ export class MainThreadCustomEditors extends Disposable implements extHostProtoc
 				}
 			}
 			return matchedWorkingCopies;
-		});
+		}));
+
+		// This reviver's only job is to activate custom editor extensions.
+		this._register(_webviewWorkbenchService.registerResolver({
+			canResolve: (webview: WebviewInput) => {
+				if (webview instanceof CustomEditorInput) {
+					extensionService.activateByEvent(`onCustomEditor:${webview.viewType}`);
+				}
+				return false;
+			},
+			resolveWebview: () => { throw new Error('not implemented'); }
+		}));
 	}
 
 	dispose() {
diff --git a/src/vs/workbench/api/browser/mainThreadWebviewPanels.ts b/src/vs/workbench/api/browser/mainThreadWebviewPanels.ts
index b089b04b6dd..32e247e848a 100644
--- a/src/vs/workbench/api/browser/mainThreadWebviewPanels.ts
+++ b/src/vs/workbench/api/browser/mainThreadWebviewPanels.ts
@@ -12,7 +12,6 @@ import * as extHostProtocol from 'vs/workbench/api/common/extHost.protocol';
 import { editorGroupToViewColumn, EditorViewColumn, viewColumnToEditorGroup } from 'vs/workbench/api/common/shared/editor';
 import { IEditorInput } from 'vs/workbench/common/editor';
 import { DiffEditorInput } from 'vs/workbench/common/editor/diffEditorInput';
-import { CustomEditorInput } from 'vs/workbench/contrib/customEditor/browser/customEditorInput';
 import { WebviewIcons } from 'vs/workbench/contrib/webview/browser/webview';
 import { WebviewInput } from 'vs/workbench/contrib/webview/browser/webviewEditorInput';
 import { ICreateWebViewShowOptions, IWebviewWorkbenchService, WebviewInputOptions } from 'vs/workbench/contrib/webview/browser/webviewWorkbenchService';
@@ -116,11 +115,6 @@ export class MainThreadWebviewPanels extends Disposable implements extHostProtoc
 		// This should trigger the real reviver to be registered from the extension host side.
 		this._register(_webviewWorkbenchService.registerResolver({
 			canResolve: (webview: WebviewInput) => {
-				if (webview instanceof CustomEditorInput) {
-					extensionService.activateByEvent(`onCustomEditor:${webview.viewType}`);
-					return false;
-				}
-
 				const viewType = this.webviewPanelViewType.toExternal(webview.viewType);
 				if (typeof viewType === 'string') {
 					extensionService.activateByEvent(`onWebviewPanel:${viewType}`);