diff --git a/mercurial/simplemerge.py b/mercurial/simplemerge.py
--- a/mercurial/simplemerge.py
+++ b/mercurial/simplemerge.py
@@ -92,7 +92,8 @@ class Merge3Text(object):
                     mid_marker='=======',
                     end_marker='>>>>>>>',
                     base_marker=None,
-                    localorother=None):
+                    localorother=None,
+                    minimize=False):
         """Return merge in cvs-like form.
         """
         self.conflicts = False
@@ -109,6 +110,8 @@ class Merge3Text(object):
         if name_base and base_marker:
             base_marker = base_marker + ' ' + name_base
         merge_regions = self.merge_regions()
+        if minimize:
+            merge_regions = self.minimize(merge_regions)
         for t in merge_regions:
             what = t[0]
             if what == 'unchanged':
@@ -441,7 +444,10 @@ def simplemerge(ui, local, base, other, 
         out = sys.stdout
 
     m3 = Merge3Text(basetext, localtext, othertext)
-    extrakwargs = {"localorother": opts.get("localorother", None)}
+    extrakwargs = {
+            "localorother": opts.get("localorother", None),
+            'minimize': True,
+        }
     if mode == 'union':
         extrakwargs['start_marker'] = None
         extrakwargs['mid_marker'] = None
@@ -449,6 +455,7 @@ def simplemerge(ui, local, base, other, 
     elif name_base is not None:
         extrakwargs['base_marker'] = '|||||||'
         extrakwargs['name_base'] = name_base
+        extrakwargs['minimize'] = False
     for line in m3.merge_lines(name_a=name_a, name_b=name_b, **extrakwargs):
         out.write(line)
 
diff --git a/tests/test-conflict.t b/tests/test-conflict.t
--- a/tests/test-conflict.t
+++ b/tests/test-conflict.t
@@ -46,16 +46,13 @@
 
   $ cat a
   Small Mathematical Series.
-  <<<<<<< local: 618808747361 - test: branch2
   1
   2
   3
+  <<<<<<< local: 618808747361 - test: branch2
   6
   8
   =======
-  1
-  2
-  3
   4
   5
   >>>>>>> other: c0c68e4fe667  - test: branch1
@@ -79,16 +76,13 @@ Verify custom conflict markers
 
   $ cat a
   Small Mathematical Series.
-  <<<<<<< local: test 2
   1
   2
   3
+  <<<<<<< local: test 2
   6
   8
   =======
-  1
-  2
-  3
   4
   5
   >>>>>>> other: test 1
@@ -108,16 +102,13 @@ Verify line splitting of custom conflict
 
   $ cat a
   Small Mathematical Series.
-  <<<<<<< local: test 2
   1
   2
   3
+  <<<<<<< local: test 2
   6
   8
   =======
-  1
-  2
-  3
   4
   5
   >>>>>>> other: test 1
@@ -150,16 +141,13 @@ Verify line trimming of custom conflict 
 
   $ cat a
   Small Mathematical Series.
-  <<<<<<< local: 123456789012345678901234567890123456789012345678901234567890\xe3\x81\x82... (esc)
   1
   2
   3
+  <<<<<<< local: 123456789012345678901234567890123456789012345678901234567890\xe3\x81\x82... (esc)
   6
   8
   =======
-  1
-  2
-  3
   4
   5
   >>>>>>> other: branch1
@@ -179,16 +167,13 @@ Verify basic conflict markers
 
   $ cat a
   Small Mathematical Series.
-  <<<<<<< local
   1
   2
   3
+  <<<<<<< local
   6
   8
   =======
-  1
-  2
-  3
   4
   5
   >>>>>>> other
diff --git a/tests/test-contrib.t b/tests/test-contrib.t
--- a/tests/test-contrib.t
+++ b/tests/test-contrib.t
@@ -148,11 +148,10 @@ conflicts
   base
   <<<<<<< conflict-local
   not other
-  end
   =======
   other
+  >>>>>>> conflict-other
   end
-  >>>>>>> conflict-other
   [1]
 
 1 label
@@ -161,11 +160,10 @@ 1 label
   base
   <<<<<<< foo
   not other
-  end
   =======
   other
+  >>>>>>> conflict-other
   end
-  >>>>>>> conflict-other
   [1]
 
 2 labels
@@ -174,11 +172,10 @@ 2 labels
   base
   <<<<<<< foo
   not other
-  end
   =======
   other
+  >>>>>>> bar
   end
-  >>>>>>> bar
   [1]
 
 3 labels
diff --git a/tests/test-rebase-conflicts.t b/tests/test-rebase-conflicts.t
--- a/tests/test-rebase-conflicts.t
+++ b/tests/test-rebase-conflicts.t
@@ -305,3 +305,55 @@ Check that the right ancestors is used w
   rebase completed
   updating the branch cache
   truncating cache/rbc-revs-v1 to 72
+
+Test minimization of merge conflicts
+  $ hg up -q null
+  $ echo a > a
+  $ hg add a
+  $ hg commit -q -m 'a'
+  $ echo b >> a
+  $ hg commit -q -m 'ab'
+  $ hg bookmark ab
+  $ hg up -q '.^'
+  $ echo b >> a
+  $ echo c >> a
+  $ hg commit -q -m 'abc'
+  $ hg rebase -s 7bc217434fc1 -d ab --keep
+  rebasing 13:7bc217434fc1 "abc" (tip)
+  merging a
+  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
+  unresolved conflicts (see hg resolve, then hg rebase --continue)
+  [1]
+  $ hg diff
+  diff -r 328e4ab1f7cc a
+  --- a/a	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/a	* (glob)
+  @@ -1,2 +1,6 @@
+   a
+   b
+  +<<<<<<< dest:   328e4ab1f7cc  ab - test: ab
+  +=======
+  +c
+  +>>>>>>> source: 7bc217434fc1 - test: abc
+  $ hg rebase --abort
+  rebase aborted
+  $ hg up -q -C 7bc217434fc1
+  $ hg rebase -s . -d ab --keep -t internal:merge3
+  rebasing 13:7bc217434fc1 "abc" (tip)
+  merging a
+  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
+  unresolved conflicts (see hg resolve, then hg rebase --continue)
+  [1]
+  $ hg diff
+  diff -r 328e4ab1f7cc a
+  --- a/a	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/a	* (glob)
+  @@ -1,2 +1,8 @@
+   a
+  +<<<<<<< dest:   328e4ab1f7cc  ab - test: ab
+   b
+  +||||||| base
+  +=======
+  +b
+  +c
+  +>>>>>>> source: 7bc217434fc1 - test: abc