diff --git a/src/ol/has.js b/src/ol/has.js
index d77ba96073..f93c1e9169 100644
--- a/src/ol/has.js
+++ b/src/ol/has.js
@@ -3,7 +3,9 @@
  */
 
 const ua =
-  typeof navigator !== 'undefined' ? navigator.userAgent.toLowerCase() : '';
+  typeof navigator !== 'undefined' && typeof navigator.userAgent !== 'undefined'
+    ? navigator.userAgent.toLowerCase()
+    : '';
 
 /**
  * User agent string says we are dealing with Firefox as browser.