diff --git a/app/assets/stylesheets/mobile/modal.scss b/app/assets/stylesheets/mobile/modal.scss
index 3111b601323..9715a193161 100644
--- a/app/assets/stylesheets/mobile/modal.scss
+++ b/app/assets/stylesheets/mobile/modal.scss
@@ -88,7 +88,8 @@
   form {
     margin-top: 20px;
     input[type=text] {
-      width: 500px;
+      box-sizing: border-box;
+      width: 100%;
     }
   }
 }