diff --git a/index.js b/index.js
index c9f8d2d5..8a1c8e33 100644
--- a/index.js
+++ b/index.js
@@ -14,6 +14,7 @@ const CDN_IMG_SELECTORS = [
   'feature-image',
   'author-profile-image',
 ]
+const RELATIVE_CONTENT_PREFIX = ENV_RELATIVE_CONTENT_PREFIX || '/content/images/'
 
 class ElementHandler {
   element(element) {
@@ -37,7 +38,7 @@ class ElementHandler {
       // If image is loaded from local content, rewrite to pull from CDN
       if (
         imgSrc.startsWith(ENV_LOCAL_CONTENT_URL) ||
-        imgSrc.startsWith(ENV_RELATIVE_CONTENT_PREFIX)
+        imgSrc.startsWith(RELATIVE_CONTENT_PREFIX)
       ) {
         element.setAttribute('src', ENV_CDN_FETCH_URL + imgSrc)
       }