diff --git a/src/vs/workbench/api/common/configurationExtensionPoint.ts b/src/vs/workbench/api/common/configurationExtensionPoint.ts
index 17516f5f860cdf407ecf5dc6267e6f34ba38c6f7..ace383a9f24174499a55f03bc6a03f1ed017b3c9 100644
--- a/src/vs/workbench/api/common/configurationExtensionPoint.ts
+++ b/src/vs/workbench/api/common/configurationExtensionPoint.ts
@@ -8,11 +8,12 @@ import * as objects from 'vs/base/common/objects';
 import { Registry } from 'vs/platform/registry/common/platform';
 import { IJSONSchema } from 'vs/base/common/jsonSchema';
 import { ExtensionsRegistry, IExtensionPointUser } from 'vs/workbench/services/extensions/common/extensionsRegistry';
-import { IConfigurationNode, IConfigurationRegistry, Extensions, resourceLanguageSettingsSchemaId, IDefaultConfigurationExtension, validateProperty, ConfigurationScope } from 'vs/platform/configuration/common/configurationRegistry';
+import { IConfigurationNode, IConfigurationRegistry, Extensions, resourceLanguageSettingsSchemaId, IDefaultConfigurationExtension, validateProperty, ConfigurationScope, OVERRIDE_PROPERTY_PATTERN } from 'vs/platform/configuration/common/configurationRegistry';
 import { IJSONContributionRegistry, Extensions as JSONExtensions } from 'vs/platform/jsonschemas/common/jsonContributionRegistry';
 import { workspaceSettingsSchemaId, launchSchemaId, tasksSchemaId } from 'vs/workbench/services/configuration/common/configuration';
 import { isObject } from 'vs/base/common/types';
 import { ExtensionIdentifier } from 'vs/platform/extensions/common/extensions';
+import { IStringDictionary } from 'vs/base/common/collections';
 
 const configurationRegistry = Registry.as<IConfigurationRegistry>(Extensions.Configuration);
 
@@ -116,7 +117,13 @@ defaultConfigurationExtPoint.setHandler((extensions, { added, removed }) => {
 		const addedDefaultConfigurations = added.map(extension => {
 			const id = extension.description.identifier;
 			const name = extension.description.name;
-			const defaults = objects.deepClone(extension.value);
+			const defaults: IStringDictionary<any> = objects.deepClone(extension.value);
+			for (const key of Object.keys(defaults)) {
+				if (!OVERRIDE_PROPERTY_PATTERN.test(key) || typeof defaults[key] !== 'object') {
+					extension.collector.warn(nls.localize('config.property.defaultConfiguration.warning', "Cannot register configuration defaults for '{0}'. Only defaults for language specific settings are supported.", key));
+					delete defaults[key];
+				}
+			}
 			return <IDefaultConfigurationExtension>{
 				id, name, defaults
 			};