diff --git a/mercurial/revlogutils/sidedata.py b/mercurial/revlogutils/sidedata.py
--- a/mercurial/revlogutils/sidedata.py
+++ b/mercurial/revlogutils/sidedata.py
@@ -49,8 +49,8 @@ SD_TEST6 = 6
 SD_TEST7 = 7
 
 # internal format constant
-SIDEDATA_HEADER = struct.Struct('>H')
-SIDEDATA_ENTRY = struct.Struct('>HL20s')
+SIDEDATA_HEADER = struct.Struct(r'>H')
+SIDEDATA_ENTRY = struct.Struct(r'>HL20s')
 
 def sidedatawriteprocessor(rl, text, sidedata):
     sidedata = list(sidedata.items())