diff --git a/src/helpers/AmpConfig.js b/src/helpers/AmpConfig.js
index 3b572e1..a3eb25d 100644
--- a/src/helpers/AmpConfig.js
+++ b/src/helpers/AmpConfig.js
@@ -30,7 +30,7 @@ const AmpConfig = (providedOptions) => {
     throw new Error(`filter needs to be a valid RegExp, provided : ${options.filter}`);
   }
 
-  options.isAmp = (path) => path.endsWith('.html') && options.filter.test(path);
+  options.isAmp = (path) => path && path.endsWith('.html') && options.filter.test(path);
 
   if (providedOptions.optimizeImages !== false && !providedOptions.imageOptimizer) {
     options.imageOptimizer = ImageOptimizer.create(options);