Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php    (revision 43647)
+++ wp-includes/taxonomy.php    (working copy)
@@ -919,6 +919,10 @@
  *                             or `$term` was not found.
  */
 function get_term_by( $field, $value, $taxonomy = '', $output = OBJECT, $filter = 'raw' ) {
+       // 'ID' is an alias of 'id'.
+       if ( 'ID' === $field ) {
+               $field = 'id';
+       }

        // 'term_taxonomy_id' lookups don't require taxonomy checks.
        if ( 'term_taxonomy_id' !== $field && ! taxonomy_exists( $taxonomy ) ) {