diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -2425,6 +2425,17 @@ class _addset(object):
             return orderedlazyset(self, filterfunc, ascending=self._ascending)
         return lazyset(self, filterfunc)
 
+    def __add__(self, other):
+        """When both collections are ascending or descending, preserve the order
+        """
+        kwargs = {}
+        if self._ascending is not None:
+            if self.isascending() and other.isascending():
+                kwargs['ascending'] = True
+            if self.isdescending() and other.isdescending():
+                kwargs['ascending'] = False
+        return _addset(self, other, **kwargs)
+
     def _iterator(self):
         """Iterate over both collections without repeating elements