diff -r af83a0ed0afb -r 32bc3815efae mercurial/hook.py
--- a/mercurial/hook.py	Thu May 10 21:00:58 2018 +0900
+++ b/mercurial/hook.py	Thu May 10 21:08:32 2018 +0900
@@ -138,7 +138,7 @@
         if callable(v):
             v = v()
         if isinstance(v, (dict, list)):
-            v = stringutil.pprint(v, bprefix=False)
+            v = stringutil.pprint(v)
         env['HG_' + k.upper()] = v
 
     if repo: