diff --git a/horizon/static/horizon/js/horizon.forms.js b/horizon/static/horizon/js/horizon.forms.js
index e202855ee4..825bf0524c 100644
--- a/horizon/static/horizon/js/horizon.forms.js
+++ b/horizon/static/horizon/js/horizon.forms.js
@@ -57,16 +57,9 @@ horizon.forms = {
         $volName.val($option.data("name"));
       }
       var $volSize = $form.find('input#id_size');
-      var volSize = parseInt($volSize.val(), 10) || -1;
       var dataSize = parseInt($option.data("size"), 10) || -1;
-      var minDiskSize = parseInt($option.data("min_disk"), 10) || -1;
-      var defaultVolSize = dataSize;
-      if (minDiskSize > defaultVolSize) {
-        defaultVolSize = minDiskSize;
-      }
-      if (volSize < defaultVolSize) {
-        $volSize.val(defaultVolSize);
-      }
+      var minDiskSize = parseInt($option.data("min_disk"), 10) || 1;
+      $volSize.val(Math.max(minDiskSize, dataSize));
     });
   },