diff --git a/mercurial/changegroup.py b/mercurial/changegroup.py
--- a/mercurial/changegroup.py
+++ b/mercurial/changegroup.py
@@ -1293,6 +1293,11 @@
         #
         # (or even to push subset of history)
         needv03 = True
+    if 'exp-sidedata-flag' in repo.requirements:
+        needv03 = True
+        # don't attempt to use 01/02 until we do sidedata cleaning
+        versions.discard('01')
+        versions.discard('02')
     if not needv03:
         versions.discard('03')
     return versions