diff --git a/web/viewer.html b/web/viewer.html
index c5195fdcf..d45bde539 100644
--- a/web/viewer.html
+++ b/web/viewer.html
@@ -239,7 +239,7 @@ See https://github.com/adobe-type-tools/cmap-resources
                     <option id="pageActualOption" title="" value="page-actual" data-l10n-id="page_scale_actual">Actual Size</option>
                     <option id="pageFitOption" title="" value="page-fit" data-l10n-id="page_scale_fit">Fit Page</option>
                     <option id="pageWidthOption" title="" value="page-width" data-l10n-id="page_scale_width">Full Width</option>
-                    <option id="customScaleOption" title="" value="custom" hidden="true"></option>
+                    <option id="customScaleOption" title="" value="custom" disabled="disabled" hidden="true"></option>
                     <option title="" value="0.5" data-l10n-id="page_scale_percent" data-l10n-args='{ "scale": 50 }'>50%</option>
                     <option title="" value="0.75" data-l10n-id="page_scale_percent" data-l10n-args='{ "scale": 75 }'>75%</option>
                     <option title="" value="1" data-l10n-id="page_scale_percent" data-l10n-args='{ "scale": 100 }'>100%</option>