diff --git a/src/vs/base/common/uri.ts b/src/vs/base/common/uri.ts
index 8111602efc5..55a39c0f372 100644
--- a/src/vs/base/common/uri.ts
+++ b/src/vs/base/common/uri.ts
@@ -108,7 +108,7 @@ export class URI implements UriComponents {
 			&& typeof (<URI>thing).path === 'string'
 			&& typeof (<URI>thing).query === 'string'
 			&& typeof (<URI>thing).scheme === 'string'
-			&& typeof (<URI>thing).fsPath === 'function'
+			&& typeof (<URI>thing).fsPath === 'string'
 			&& typeof (<URI>thing).with === 'function'
 			&& typeof (<URI>thing).toString === 'function';
 	}