diff --git a/src/testdir/test_langmap.vim b/src/testdir/test_langmap.vim
index 420ff0f..4f831aa 100644
--- a/src/testdir/test_langmap.vim
+++ b/src/testdir/test_langmap.vim
@@ -23,5 +23,32 @@
   silent! call feedkeys("gg0}%}\<C-G>}^\<Esc>00", 'tx')
   call assert_equal('a}^de', getline(1))
 
+  " Error cases
+  call assert_fails('set langmap=aA,b', 'E357:')
+  call assert_fails('set langmap=z;y;y;z', 'E358:')
+
+  " Map character > 256
+  enew!
+  set langmap=āx,ăl,āx
+  call setline(1, ['abcde'])
+  call feedkeys('gg2lā', 'tx')
+  call assert_equal('abde', getline(1))
+
+  " special characters in langmap
+  enew!
+  call setline(1, ['Hello World'])
+  set langmap=\\;\\,,\\,\\;
+  call feedkeys('ggfo,', 'tx')
+  call assert_equal(8, col('.'))
+  call feedkeys(';', 'tx')
+  call assert_equal(5, col('.'))
+  set langmap&
+  set langmap=\\;\\,;\\,\\;
+  call feedkeys('ggfo,', 'tx')
+  call assert_equal(8, col('.'))
+  call feedkeys(';', 'tx')
+  call assert_equal(5, col('.'))
+
+  set langmap&
   quit!
 endfunc