Index: wp-includes/default-widgets.php
===================================================================
--- wp-includes/default-widgets.php	(revision 23185)
+++ wp-includes/default-widgets.php	(working copy)
@@ -723,7 +723,7 @@
 		<input class="widefat" id="<?php echo $this->get_field_id('title'); ?>" name="<?php echo $this->get_field_name('title'); ?>" type="text" value="<?php echo $title; ?>" /></p>
 
 		<p><label for="<?php echo $this->get_field_id('number'); ?>"><?php _e('Number of comments to show:'); ?></label>
-		<input id="<?php echo $this->get_field_id('number'); ?>" name="<?php echo $this->get_field_name('number'); ?>" type="text" value="<?php echo $number; ?>" size="3" /></p>
+		<input class="small-text" id="<?php echo $this->get_field_id('number'); ?>" name="<?php echo $this->get_field_name('number'); ?>" type="number" step="1" min="1" value="<?php echo $number; ?>" size="3" /></p>
 <?php
 	}
 }