diff -r d532292eff22 -r b6387a65851d mercurial/utils/cborutil.py
--- a/mercurial/utils/cborutil.py	Fri May 31 22:37:14 2019 -0700
+++ b/mercurial/utils/cborutil.py	Sun Jun 16 12:31:07 2019 +0900
@@ -214,6 +214,14 @@
     fn = STREAM_ENCODERS.get(v.__class__)
 
     if not fn:
+        # handle subtypes such as encoding.localstr and util.sortdict
+        for ty in STREAM_ENCODERS:
+            if not isinstance(v, ty):
+                continue
+            fn = STREAM_ENCODERS[ty]
+            break
+
+    if not fn:
         raise ValueError('do not know how to encode %s' % type(v))
 
     return fn(v)