Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 17357)
+++ wp-includes/taxonomy.php	(working copy)
@@ -877,15 +877,24 @@
 	if ( ! taxonomy_exists($taxonomy) )
 		return false;
 
-	if ( 'slug' == $field ) {
+	if ( '_slug' == $field ) {
 		$field = 't.slug';
-		$value = sanitize_title($value);
 		if ( empty($value) )
 			return false;
+
+	} else if ( 'slug' == $field ) {
+		$san_title = sanitize_title($value);
+		$san_title_query = sanitize_title_for_query($value);
+		$term = get_term_by('_slug', $san_title, $taxonomy, $output, $filter);
+		if ( empty($term) && $san_title != $san_title_query )
+			$term = get_term_by('_slug', $san_title_query, $taxonomy, $output, $filter);
+		return $term;
+
 	} else if ( 'name' == $field ) {
 		// Assume already escaped
 		$value = stripslashes($value);
 		$field = 't.name';
+
 	} else {
 		return get_term( (int) $value, $taxonomy, $output, $filter);
 	}