diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -1587,7 +1587,8 @@ class changeset_templater(changeset_prin
         self._tref = tmplspec.ref
         self._parts = {'header': '', 'footer': '',
                        tmplspec.ref: tmplspec.ref,
-                       'docheader': '', 'docfooter': ''}
+                       'docheader': '', 'docfooter': '',
+                       'separator': ''}
         if tmplspec.mapfile:
             # find correct templates for current mode, for backward
             # compatibility with 'log -v/-q/--debug' using a mapfile
@@ -1621,11 +1622,17 @@ class changeset_templater(changeset_prin
         props['ctx'] = ctx
         props['repo'] = self.repo
         props['ui'] = self.repo.ui
-        props['index'] = next(self._counter)
+        props['index'] = index = next(self._counter)
         props['revcache'] = {'copies': copies}
         props['cache'] = self.cache
         props = pycompat.strkwargs(props)
 
+        # write separator, which wouldn't work well with the header part below
+        # since there's inherently a conflict between header (across items) and
+        # separator (per item)
+        if self._parts['separator'] and index > 0:
+            self.ui.write(templater.stringify(self.t(self._parts['separator'])))
+
         # write header
         if self._parts['header']:
             h = templater.stringify(self.t(self._parts['header'], **props))
diff --git a/tests/test-command-template.t b/tests/test-command-template.t
--- a/tests/test-command-template.t
+++ b/tests/test-command-template.t
@@ -257,6 +257,20 @@ Test template map inheritance
   summary:     third
   
 
+Test docheader, docfooter and separator in template map
+
+  $ cat <<'EOF' > map-myjson
+  > docheader = '\{\n'
+  > docfooter = '\n}\n'
+  > separator = ',\n'
+  > changeset = ' {dict(rev, node|short)|json}'
+  > EOF
+  $ hg log -l2 -T./map-myjson
+  {
+   {"node": "95c24699272e", "rev": 8},
+   {"node": "29114dbae42b", "rev": 7}
+  }
+
 Template should precede style option
 
   $ hg log -l1 --style default -T '{rev}\n'