diff -r b409cdc6a139 -r 5554aacd783f mercurial/revlog.py
--- a/mercurial/revlog.py	Tue Mar 30 17:03:02 2021 +0200
+++ b/mercurial/revlog.py	Thu Apr 08 16:39:39 2021 +0200
@@ -2246,7 +2246,7 @@
 
         deltainfo = deltacomputer.finddeltainfo(revinfo, fh)
 
-        if sidedata:
+        if sidedata and self.version & 0xFFFF == REVLOGV2:
             serialized_sidedata = sidedatautil.serialize_sidedata(sidedata)
             sidedata_offset = offset + deltainfo.deltalen
         else: