diff --git a/step39_generators/app.ts b/step39_generators/app.ts
index 3e0b14d5..aba050a0 100644
--- a/step39_generators/app.ts
+++ b/step39_generators/app.ts
@@ -1,6 +1,6 @@
 //Execution of a generator is paused till the next iteration is invoked
 
-function *generatorFn(): string{
+function *generatorFn(): Generator<string> {
     //first task
     yield "firstValue";