diff --git a/src/vs/platform/extensions/common/extensions.ts b/src/vs/platform/extensions/common/extensions.ts
index e3b96a680ed..00747129b0e 100644
--- a/src/vs/platform/extensions/common/extensions.ts
+++ b/src/vs/platform/extensions/common/extensions.ts
@@ -23,7 +23,7 @@ export interface IExtensionDescription {
 	};
 	readonly main?: string;
 	readonly contributes?: { [point: string]: any; };
-	readonly enableProposedApi: boolean;
+	readonly enableProposedApi?: boolean;
 }
 
 export const IExtensionService = createDecorator<IExtensionService>('extensionService');
diff --git a/src/vs/workbench/node/extensionPoints.ts b/src/vs/workbench/node/extensionPoints.ts
index 94b95832ba5..6b47f5be174 100644
--- a/src/vs/workbench/node/extensionPoints.ts
+++ b/src/vs/workbench/node/extensionPoints.ts
@@ -211,7 +211,7 @@ class ExtensionManifestValidator extends ExtensionManifestHandler {
 				vscode: string;
 			};
 			main?: string;
-			enableProposedApi: boolean;
+			enableProposedApi?: boolean;
 		}
 		let extensionDescription = <IRelaxedExtensionDescription>_extensionDescription;
 		extensionDescription.isBuiltin = this._isBuiltin;
diff --git a/src/vs/workbench/parts/debug/test/node/debugAdapter.test.ts b/src/vs/workbench/parts/debug/test/node/debugAdapter.test.ts
index 07133c7514d..426a1052499 100644
--- a/src/vs/workbench/parts/debug/test/node/debugAdapter.test.ts
+++ b/src/vs/workbench/parts/debug/test/node/debugAdapter.test.ts
@@ -49,7 +49,7 @@ suite('Debug - Adapter', () => {
 	};
 
 	setup(() => {
-		adapter = new Adapter(rawAdapter, { extensionFolderPath, id: 'adapter', name: 'myAdapter', version: '1.0.0', publisher: 'vscode', isBuiltin: false, engines: null, enableProposedApi: false }, null, null, null);
+		adapter = new Adapter(rawAdapter, { extensionFolderPath, id: 'adapter', name: 'myAdapter', version: '1.0.0', publisher: 'vscode', isBuiltin: false, engines: null }, null, null, null);
 	});
 
 	teardown(() => {