diff --git a/src/vs/workbench/api/node/extHostConfiguration.ts b/src/vs/workbench/api/node/extHostConfiguration.ts
index c7c10c31fb2..fb1ac12bc09 100644
--- a/src/vs/workbench/api/node/extHostConfiguration.ts
+++ b/src/vs/workbench/api/node/extHostConfiguration.ts
@@ -100,6 +100,10 @@ export class ExtHostConfiguration implements ExtHostConfigurationShape {
 					let clonedConfig = void 0;
 					const cloneOnWriteProxy = (target: any, accessor: string): any => {
 						let clonedTarget = void 0;
+						const cloneTarget = () => {
+							clonedConfig = clonedConfig ? clonedConfig : deepClone(config);
+							clonedTarget = clonedTarget ? clonedTarget : lookUp(clonedConfig, accessor);
+						};
 						return isObject(target) ?
 							new Proxy(target, {
 								get: (target: any, property: string) => {
@@ -114,10 +118,19 @@ export class ExtHostConfiguration implements ExtHostConfigurationShape {
 									return result;
 								},
 								set: (target: any, property: string, value: any) => {
-									clonedConfig = clonedConfig ? clonedConfig : deepClone(config);
-									clonedTarget = clonedTarget ? clonedTarget : lookUp(clonedConfig, accessor);
+									cloneTarget();
 									clonedTarget[property] = value;
 									return true;
+								},
+								deleteProperty: (target: any, property: string) => {
+									cloneTarget();
+									delete clonedTarget[property];
+									return true;
+								},
+								defineProperty: (target: any, property: string, descriptor: any) => {
+									cloneTarget();
+									Object.defineProperty(clonedTarget, property, descriptor);
+									return true;
 								}
 							}) : target;
 					};
diff --git a/src/vs/workbench/test/electron-browser/api/extHostConfiguration.test.ts b/src/vs/workbench/test/electron-browser/api/extHostConfiguration.test.ts
index b7008d3f5a0..382cbc08b75 100644
--- a/src/vs/workbench/test/electron-browser/api/extHostConfiguration.test.ts
+++ b/src/vs/workbench/test/electron-browser/api/extHostConfiguration.test.ts
@@ -102,6 +102,11 @@ suite('ExtHostConfiguration', function () {
 					'config2': 'Das Pferd frisst kein Reis.'
 				},
 				'config4': ''
+			},
+			'workbench': {
+				'colorCustomizations': {
+					'statusBar.foreground': 'somevalue'
+				}
 			}
 		});
 
@@ -131,6 +136,14 @@ suite('ExtHostConfiguration', function () {
 		actual = testObject.inspect('farboo');
 		actual['value'] = 'effectiveValue';
 		assert.equal('effectiveValue', actual['value']);
+
+		testObject = all.getConfiguration('workbench');
+		actual = testObject.get('colorCustomizations');
+		delete actual['statusBar.foreground'];
+		assert.equal(actual['statusBar.foreground'], undefined);
+		testObject = all.getConfiguration('workbench');
+		actual = testObject.get('colorCustomizations');
+		assert.equal(actual['statusBar.foreground'], 'somevalue');
 	});
 
 	test('cannot modify returned configuration', function () {
@@ -158,7 +171,6 @@ suite('ExtHostConfiguration', function () {
 			testObject['farboo']['config0'] = false;
 			assert.fail('This should be readonly');
 		} catch (e) {
-			console.log(e);
 		}
 
 		try {