diff --git a/src/lib/FastImageSequence.ts b/src/lib/FastImageSequence.ts
index 08bcbc2..c53228d 100644
--- a/src/lib/FastImageSequence.ts
+++ b/src/lib/FastImageSequence.ts
@@ -3,7 +3,7 @@ import Frame from "./Frame.js";
 import {ImageFetchWorker} from "./ImageFetchWorker.js";
 
 export function isMobile(): boolean {
-  return /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent);
+  return (typeof navigator !== "undefined" && /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent));
 }
 
 /**