diff --git a/completed/CountdownTimer/app/components/Countdown.jsx b/completed/CountdownTimer/app/components/Countdown.jsx
index b4e969b..f11e0a8 100644
--- a/completed/CountdownTimer/app/components/Countdown.jsx
+++ b/completed/CountdownTimer/app/components/Countdown.jsx
@@ -23,9 +23,11 @@ class Countdown extends React.Component {
 
     tick() {
         this.timer = setInterval(() => {
-            var newCount = this.state.count - 1;
-            this.setState({
-                count: newCount >= 0 ? newCount : 0
+            this.setState(oldState => {
+                const newCount = this.state.count - 1;
+                return {
+                    count: newCount >= 0 ? newCount : 0
+                };
             });
         }, 1000);
     }
diff --git a/completed_with_auth0/CountdownTimer/app/components/Countdown.jsx b/completed_with_auth0/CountdownTimer/app/components/Countdown.jsx
index b4e969b..f11e0a8 100644
--- a/completed_with_auth0/CountdownTimer/app/components/Countdown.jsx
+++ b/completed_with_auth0/CountdownTimer/app/components/Countdown.jsx
@@ -23,9 +23,11 @@ class Countdown extends React.Component {
 
     tick() {
         this.timer = setInterval(() => {
-            var newCount = this.state.count - 1;
-            this.setState({
-                count: newCount >= 0 ? newCount : 0
+            this.setState(oldState => {
+                const newCount = this.state.count - 1;
+                return {
+                    count: newCount >= 0 ? newCount : 0
+                };
             });
         }, 1000);
     }
diff --git a/starter/CountdownTimer/app/components/Countdown.jsx b/starter/CountdownTimer/app/components/Countdown.jsx
index b4e969b..f11e0a8 100644
--- a/starter/CountdownTimer/app/components/Countdown.jsx
+++ b/starter/CountdownTimer/app/components/Countdown.jsx
@@ -23,9 +23,11 @@ class Countdown extends React.Component {
 
     tick() {
         this.timer = setInterval(() => {
-            var newCount = this.state.count - 1;
-            this.setState({
-                count: newCount >= 0 ? newCount : 0
+            this.setState(oldState => {
+                const newCount = this.state.count - 1;
+                return {
+                    count: newCount >= 0 ? newCount : 0
+                };
             });
         }, 1000);
     }