diff --git a/caption_filter.module b/caption_filter.module
index 2ca7d0d..4e7188a 100644
--- a/caption_filter.module
+++ b/caption_filter.module
@@ -114,9 +114,12 @@ function _caption_filter_get_width($item) {
   unset($src_result, $width_result, $internal_result, $tag, $item);
 
   // We need to append the 'px' to any numeric widths.
-  if (is_numeric($width)) {
+  if (isset($width) && is_numeric($width)) {
     $width = $width . 'px';
   }
+  else {
+    $width = NULL;
+  }
 
   return $width;
 }