diff --git a/includes/sanitizers/class-amp-core-theme-sanitizer.php b/includes/sanitizers/class-amp-core-theme-sanitizer.php
index 8518f8d3db8..166a275ca43 100644
--- a/includes/sanitizers/class-amp-core-theme-sanitizer.php
+++ b/includes/sanitizers/class-amp-core-theme-sanitizer.php
@@ -1030,6 +1030,12 @@ static function() use ( $args ) {
 						}
 					}
 
+					@media (max-width: 999px) {
+						amp-lightbox.cover-modal.show-modal {
+							display: unset;
+						}
+					}
+
 				}
 				<?php elseif ( 'twentyseventeen' === get_template() ) : ?>
 					/* Show the button*/