diff --git a/src/util/rb_tree.h b/src/util/rb_tree.h
index a7ee296681..6b4de0c89d 100644
--- a/src/util/rb_tree.h
+++ b/src/util/rb_tree.h
@@ -483,6 +483,9 @@ rb_tree<T, CMP> erase(rb_tree<T, CMP> const & t, T const & v) { rb_tree<T, CMP>
 struct unsigned_cmp {
     int operator()(unsigned i1, unsigned i2) const { return i1 < i2 ? -1 : (i1 == i2 ? 0 : 1); }
 };
+struct unsigned_rev_cmp {
+    int operator()(unsigned i1, unsigned i2) const { return i1 > i2 ? -1 : (i1 == i2 ? 0 : 1); }
+};
 struct int_cmp {
     int operator()(int i1, int i2) const { return i1 < i2 ? -1 : (i1 == i2 ? 0 : 1); }
 };