diff --git a/src/decorator-observable.js b/src/decorator-observable.js
index 21c1d829..0fd6dca7 100644
--- a/src/decorator-observable.js
+++ b/src/decorator-observable.js
@@ -12,7 +12,7 @@ export function observable(targetOrConfig: any, key: string, descriptor?: Proper
     const innerPropertyDescriptor: PropertyDescriptor = {
       configurable: true,
       enumerable: false,
-      writable: true,
+      writable: true
     };
 
     // determine callback name based on config or convention.