diff --git a/mercurial/pure/charencode.py b/mercurial/pure/charencode.py
--- a/mercurial/pure/charencode.py
+++ b/mercurial/pure/charencode.py
@@ -74,6 +74,6 @@ def jsonescapeu8fallback(u8chars, parano
     else:
         jm = _jsonmap
     # non-BMP char is represented as UTF-16 surrogate pair
-    u16codes = array.array('H', u8chars.decode('utf-8').encode('utf-16'))
+    u16codes = array.array(r'H', u8chars.decode('utf-8').encode('utf-16'))
     u16codes.pop(0)  # drop BOM
     return ''.join(jm[x] if x < 128 else '\\u%04x' % x for x in u16codes)