diff --git a/src/vs/workbench/contrib/tasks/common/taskConfiguration.ts b/src/vs/workbench/contrib/tasks/common/taskConfiguration.ts
index 515edd44738b6d86d559aa8eeb43067f3c46bddf..528b95b01342ce63de64e248ff43d702ebd2d6f2 100644
--- a/src/vs/workbench/contrib/tasks/common/taskConfiguration.ts
+++ b/src/vs/workbench/contrib/tasks/common/taskConfiguration.ts
@@ -1242,11 +1242,11 @@ namespace ConfigurationProperties {
 		{ property: 'presentation', type: CommandConfiguration.PresentationOptions }, { property: 'problemMatchers' }
 	];
 
-	export function from(this: void, external: ConfigurationProperties, context: ParseContext, includeCommandOptions: boolean, properties?: IJSONSchemaMap): Tasks.ConfigurationProperties | undefined {
+	export function from(this: void, external: ConfigurationProperties & { [key: string]: any; }, context: ParseContext, includeCommandOptions: boolean, properties?: IJSONSchemaMap): Tasks.ConfigurationProperties | undefined {
 		if (!external) {
 			return undefined;
 		}
-		let result: Tasks.ConfigurationProperties = {};
+		let result: Tasks.ConfigurationProperties & { [key: string]: any; } = {};
 
 		if (properties) {
 			for (const propertyName of Object.keys(properties)) {