diff --git a/SensitiveContentPlugin.php b/SensitiveContentPlugin.php
index 5054d5a..8447ae9 100644
--- a/SensitiveContentPlugin.php
+++ b/SensitiveContentPlugin.php
@@ -166,8 +166,8 @@ EOB;
 		} catch (Exception $e) {
 			$thumbnail = null;
 		}
-		$thumbWidthCss = $thumbnail ? $thumbnail->width.'px' : 'auto';
-		$thumbHeightCss = $thumbnail ? $thumbnail->height.'px' : 'auto';
+		$thumbWidthCss = $thumbnail ? $thumbnail->width.'px' : '100%';
+		$thumbHeightCss = $thumbnail ? $thumbnail->height.'px' : '100%';
 
 		$out->elementStart('div', array(
 			'class'=>'attachment-wrapper',