--- a/mercurial/commands.py	Wed Mar 02 10:42:58 2016 +0000
+++ b/mercurial/commands.py	Sun Feb 14 07:35:50 2016 +0000
@@ -1720,6 +1720,15 @@
         if not allowunstable and old.children():
             raise error.Abort(_('cannot amend changeset with children'))
 
+        # Currently histedit gets confused if an amend happens while histedit
+        # is in progress. Since we have a checkunfinished command, we are
+        # temporarily honoring it.
+        #
+        # Note: eventually this guard will be removed. Please do not expect
+        # this behavior to remain.
+        if not obsolete.isenabled(repo, obsolete.createmarkersopt):
+            cmdutil.checkunfinished(repo)
+
         # commitfunc is used only for temporary amend commit by cmdutil.amend
         def commitfunc(ui, repo, message, match, opts):
             return repo.commit(message,

--- a/tests/test-histedit-arguments.t	Wed Mar 02 10:42:58 2016 +0000
+++ b/tests/test-histedit-arguments.t	Sun Feb 14 07:35:50 2016 +0000
@@ -450,3 +450,46 @@
   > pick 6f2f0241f119
   > pick 8cde254db839
   > EOF
+
+commit --amend should abort if histedit is in progress
+(issue4800) and markers are not being created.
+Eventually, histedit could perhaps look at `source` extra,
+in which case this test should be revisited.
+
+  $ hg -q up 8cde254db839
+  $ hg histedit 6f2f0241f119 --commands - <<EOF
+  > pick 8cde254db839
+  > edit 6f2f0241f119
+  > EOF
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  merging foo
+  warning: conflicts while merging foo! (edit, then use 'hg resolve --mark')
+  Fix up the change (pick 8cde254db839)
+  (hg histedit --continue to resume)
+  [1]
+  $ hg resolve -m --all
+  (no more unresolved files)
+  continue: hg histedit --continue
+  $ hg histedit --cont
+  merging foo
+  warning: conflicts while merging foo! (edit, then use 'hg resolve --mark')
+  Editing (6f2f0241f119), you may commit or record as needed now.
+  (hg histedit --continue to resume)
+  [1]
+  $ hg resolve -m --all
+  (no more unresolved files)
+  continue: hg histedit --continue
+  $ hg commit --amend -m 'reject this fold'
+  abort: histedit in progress
+  (use 'hg histedit --continue' or 'hg histedit --abort')
+  [255]
+
+With markers enabled, histedit does not get confused, and
+amend should not be blocked by the ongoing histedit.
+
+  $ cat >>$HGRCPATH <<EOF
+  > [experimental]
+  > evolution=createmarkers,allowunstable
+  > EOF
+  $ hg commit --amend -m 'allow this fold'
+  $ hg histedit --continue