diff --git a/src/index.js b/src/index.js
index 191ed7d..124014b 100644
--- a/src/index.js
+++ b/src/index.js
@@ -15,5 +15,7 @@ const stores = {
   memory: memory(),
 }
 
-window.Study = Study
+if (typeof window !== undefined) {
+  window.Study = Study
+}
 Study.stores = stores