diff --git a/source/image-handler/image-request.js b/source/image-handler/image-request.js
index 2a47530da..dbd252dfe 100644
--- a/source/image-handler/image-request.js
+++ b/source/image-handler/image-request.js
@@ -287,7 +287,7 @@ class ImageRequest {
     * @param {Object} event - The request body.
     */
     getOutputFormat(event) {
-        const autoWebP = process.env.AUTO_WEBP;
+        const autoWebP = (process.env.AUTO_WEBP === "Yes");
         if (autoWebP && event.headers.Accept && event.headers.Accept.includes('image/webp')) {
             return 'webp';
         } else if (this.requestType === 'Default') {
diff --git a/source/image-handler/test/test-image-request.js b/source/image-handler/test/test-image-request.js
index 9507dacef..8662638f1 100644
--- a/source/image-handler/test/test-image-request.js
+++ b/source/image-handler/test/test-image-request.js
@@ -689,7 +689,7 @@ describe('getOutputFormat()', function () {
         it(`Should pass if it returns "webp" for an accepts header which includes webp`, function () {
             // Arrange
             process.env = {
-                AUTO_WEBP: true
+                AUTO_WEBP: "Yes"
             };
             const event = {
                 headers: {
@@ -707,7 +707,7 @@ describe('getOutputFormat()', function () {
         it(`Should pass if it returns null for an accepts header which does not include webp`, function () {
             // Arrange
             process.env = {
-                AUTO_WEBP: true
+                AUTO_WEBP: "Yes"
             };
             const event = {
                 headers: {
@@ -725,7 +725,7 @@ describe('getOutputFormat()', function () {
         it(`Should pass if it returns null when AUTO_WEBP is disabled with accepts header including webp`, function () {
             // Arrange
             process.env = {
-                AUTO_WEBP: false
+                AUTO_WEBP: "No"
             };
             const event = {
                 headers: {