diff --git a/src/screen.c b/src/screen.c
index dc5d175d8a2597..8a66fc2f3d3fb1 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -4910,7 +4910,18 @@ win_line(
 				    && vim_strchr(wp->w_p_cocu, 'v') == NULL))
 	    {
 		char_attr = conceal_attr;
-		if (prev_syntax_id != syntax_seqnr
+		/* PROBLEM: When trying to show cchar by matchadd(),
+		 * prev_syntax_id and syntax_seqnr might be 0 with :syntax off.
+		 * When trying to show cchar by :syntax match, it's no problem because
+		 * syntax_seqnr is not 0.
+		 * To support showing cchar by matchadd(), change syntax_seqnr
+		 * value to non-zero.
+		 * XXX: better solution?
+		 **/
+		if (has_match_conc && syntax_seqnr == 0)
+		    syntax_seqnr = -1;
+
+		if ((prev_syntax_id != syntax_seqnr)
 			&& (syn_get_sub_char() != NUL || match_conc
 							 || wp->w_p_cole == 1)
 			&& wp->w_p_cole != 3)
diff --git a/src/testdir/test_alot.vim b/src/testdir/test_alot.vim
index 1eb76a6decbec8..91a18223701bbe 100644
--- a/src/testdir/test_alot.vim
+++ b/src/testdir/test_alot.vim
@@ -16,6 +16,7 @@ source test_help_tagjump.vim
 source test_join.vim
 source test_lispwords.vim
 source test_matchstrpos.vim
+source test_matchadd_conceal.vim
 source test_menu.vim
 source test_partial.vim
 source test_reltime.vim
diff --git a/src/testdir/test_matchadd_conceal.vim b/src/testdir/test_matchadd_conceal.vim
new file mode 100644
index 00000000000000..c799effe5949e2
--- /dev/null
+++ b/src/testdir/test_matchadd_conceal.vim
@@ -0,0 +1,306 @@
+if !has('conceal')
+  finish
+endif
+
+fu! ScreenAttr(line, pos, eval)
+  let g:attr=[]
+  for col in a:pos
+    call add(g:attr, screenattr(a:line,col))
+  endfor
+  " In case all values are zero, probably the terminal
+  " isn't set correctly, so catch that case
+  let null = (eval(join(g:attr, '+')) == 0)
+  let str=substitute(a:eval, '\d\+', 'g:attr[&]', 'g')
+  if null || eval(str)
+    let g:attr_test="OK: ". str
+  else
+    let g:attr_test="FAILED: ".str
+    let g:attr_test.="\n". join(g:attr, ' ')
+    let g:attr_test.="\n TERM: ". &term
+  endif
+endfu
+
+function! s:screenline(lnum) abort
+  let line = []
+  for c in range(1, winwidth(0))
+    call add(line, nr2char(screenchar(a:lnum, c)))
+  endfor
+  return s:trim(join(line, ''))
+endfunction
+
+function! s:trim(str) abort
+  return matchstr(a:str,'^\s*\zs.\{-}\ze\s*$')
+endfunction
+
+function! Test_simple_matchadd()
+  new
+
+  1put='# This is a Test'
+  "             1234567890123456
+  let expect = '# This is a Test'
+
+  call cursor(1, 1)
+  call matchadd('Conceal', '\%2l ')
+  redraw!
+  let lnum = 2
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1) !=# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1) ==# screenattr(lnum, 16))
+
+  quit!
+endfunction
+
+function! Test_simple_matchadd_and_conceal()
+  new
+  setlocal concealcursor=n conceallevel=1
+
+  1put='# This is a Test'
+  "             1234567890123456
+  let expect = '#XThisXisXaXTest'
+
+  call cursor(1, 1)
+  call matchadd('Conceal', '\%2l ', 10, -1, {'conceal': 'X'})
+  redraw!
+  let lnum = 2
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1) !=# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1) ==# screenattr(lnum, 16))
+
+  quit!
+endfunction
+
+function! Test_matchadd_and_conceallevel_3()
+  new
+
+  setlocal conceallevel=3
+  " set filetype and :syntax on to change screenattr()
+  setlocal filetype=conf
+  syntax on
+
+  1put='# This is a Test'
+  "             1234567890123456
+  let expect = '#ThisisaTest'
+
+  call cursor(1, 1)
+  call matchadd('Conceal', '\%2l ', 10, -1, {'conceal': 'X'})
+  redraw!
+  let lnum = 2
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1) ==# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1) !=# screenattr(lnum, 16))
+
+  " more matchadd()
+  "             1234567890123456
+  let expect = '#Thisisa Test'
+
+  call matchadd('ErrorMsg', '\%2l Test', 20, -1, {'conceal': 'X'})
+  redraw!
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1)  ==# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2)  ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 1)  !=# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 10) ==# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1)  !=# screenattr(lnum, 16))
+  call assert_true(screenattr(lnum, 10) !=# screenattr(lnum, 16))
+
+  syntax off
+  quit!
+endfunction
+
+function! Test_default_conceal_char()
+  new
+  setlocal concealcursor=n conceallevel=1
+
+  1put='# This is a Test'
+  "             1234567890123456
+  let expect = '# This is a Test'
+
+  call cursor(1, 1)
+  call matchadd('Conceal', '\%2l ', 10, -1, {})
+  redraw!
+  let lnum = 2
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1) !=# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1) ==# screenattr(lnum, 16))
+
+  "             1234567890123456
+  let expect = '#+This+is+a+Test'
+  let listchars_save = &listchars
+  set listchars=conceal:+
+  redraw!
+
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1) !=# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1) ==# screenattr(lnum, 16))
+
+  let &listchars = listchars_save
+  quit!
+endfunction
+
+function! Test_syn_and_match_conceal()
+  new
+  setlocal concealcursor=n conceallevel=1
+
+  1put='# This is a Test'
+  "             1234567890123456
+  let expect = '#ZThisZisZaZTest'
+
+  call cursor(1, 1)
+  call matchadd('Conceal', '\%2l ', 10, -1, {'conceal': 'Z'})
+  syntax match MyConceal /\%2l / conceal containedin=ALL cchar=*
+  redraw!
+  let lnum = 2
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1) !=# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1) ==# screenattr(lnum, 16))
+
+  "             1234567890123456
+  let expect = '#*This*is*a*Test'
+  call clearmatches()
+  redraw!
+
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1) !=# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1) ==# screenattr(lnum, 16))
+
+  syntax off
+  quit!
+endfunction
+
+function! Test_clearmatches()
+  new
+  setlocal concealcursor=n conceallevel=1
+
+  1put='# This is a Test'
+  "             1234567890123456
+  let expect = '# This is a Test'
+
+  call cursor(1, 1)
+  call matchadd('Conceal', '\%2l ', 10, -1, {'conceal': 'Z'})
+  let a = getmatches()
+  call clearmatches()
+  redraw!
+
+  let lnum = 2
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1) ==# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1) ==# screenattr(lnum, 16))
+
+  " reset match using setmatches()
+  "             1234567890123456
+  let expect = '#ZThisZisZaZTest'
+  call setmatches(a)
+  redraw!
+
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1) !=# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1) ==# screenattr(lnum, 16))
+  call assert_equal({'group': 'Conceal', 'pattern': '\%2l ', 'priority': 10, 'id': a[0].id, 'conceal': 'Z'}, a[0])
+
+  quit!
+endfunction
+
+function! Test_using_matchaddpos()
+  new
+  setlocal concealcursor=n conceallevel=1
+  " set filetype and :syntax on to change screenattr()
+  setlocal filetype=conf
+  syntax on
+
+  1put='# This is a Test'
+  "             1234567890123456
+  let expect = '#Pis a Test'
+
+  call cursor(1, 1)
+  call matchaddpos('Conceal', [[2,2,6]], 10, -1, {'conceal': 'P'})
+  let a = getmatches()
+  redraw!
+
+  let lnum = 2
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1)  !=# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2)  !=# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 1)  ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 1)  ==# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 1)  !=# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1)  !=# screenattr(lnum, 16))
+  call assert_true(screenattr(lnum, 12) ==# screenattr(lnum, 16))
+  call assert_equal({'group': 'Conceal', 'id': a[0].id, 'priority': 10, 'pos1': [2, 2, 6], 'conceal': 'P'}, a[0])
+
+  syntax off
+  quit!
+endfunction
+
+function! Test_match_using_multibyte_conceal_char()
+  so mbyte.vim
+  if &enc !=? 'utf-8'
+    return
+  endif
+
+  new
+  setlocal concealcursor=n conceallevel=1
+
+  1put='# This is a Test'
+  "             1234567890123456
+  let expect = '#ˑThisˑisˑaˑTest'
+
+  call cursor(1, 1)
+  call matchadd('Conceal', '\%2l ', 20, -1, {'conceal': "\u02d1"})
+  redraw!
+
+  let lnum = 2
+  call assert_equal(expect, s:screenline(lnum))
+  call assert_true(screenattr(lnum, 1) !=# screenattr(lnum, 2))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 7))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 10))
+  call assert_true(screenattr(lnum, 2) ==# screenattr(lnum, 12))
+  call assert_true(screenattr(lnum, 1) ==# screenattr(lnum, 16))
+
+  quit!
+endfunction
+
+function! Test_matchadd_repeat_conceal_without_syntax()
+  new
+
+  " To test targets in the same line string is replaced with conceal char
+  " correctly, repeat 'TARGET'
+  1put ='TARGET_TARGETTARGET'
+  call cursor(1, 1)
+  redraw
+  call assert_equal('TARGET_TARGETTARGET', s:screenline(2))
+
+  setlocal conceallevel=2
+  call matchadd('Conceal', 'TARGET', 10, -1, {'conceal': 't'})
+
+  redraw
+  call assert_equal('t_tt', s:screenline(2))
+
+  quit!
+endfunction
diff --git a/src/testdir/test_undolevels.vim b/src/testdir/test_undolevels.vim
index 7bb25effb5297d..5da14b5b70e1b7 100644
--- a/src/testdir/test_undolevels.vim
+++ b/src/testdir/test_undolevels.vim
@@ -41,4 +41,7 @@ func Test_global_local_undolevels()
   call assert_equal(50, &g:undolevels)
   call assert_equal(-123456, &l:undolevels)
 
+  " Drop created windows
+  new
+  only!
 endfunc