diff --git a/lib/real-device-management.js b/lib/real-device-management.js
index 8fc2c59ef..768e6be5f 100644
--- a/lib/real-device-management.js
+++ b/lib/real-device-management.js
@@ -88,7 +88,8 @@ export function applySafariStartupArgs() {
     return false;
   }
 
-  const args = _.toPairs(_.mapKeys(prefs, (value, key) => _.startsWith(key, '-') ? key : `-${key}`));
+  const args = _.toPairs(prefs)
+    .map(([key, value]) => [_.startsWith(key, '-') ? key : `-${key}`, String(value)]);
   this.log.debug(`Generated Safari command line arguments: ${args.join(' ')}`);
   if (_.isPlainObject(this.opts.processArguments)) {
     this.opts.processArguments.args = [...(this.opts.processArguments.args ?? []), ...args];