diff --git a/src/testdir/test_utf8.vim b/src/testdir/test_utf8.vim
index d71d7ad..9ad7828 100644
--- a/src/testdir/test_utf8.vim
+++ b/src/testdir/test_utf8.vim
@@ -167,6 +167,39 @@
   call assert_equal(2, strwidth("\u1339"))
   call assert_equal(1, strwidth("\u133a"))
 
+  for aw in ['single', 'double']
+    exe 'set ambiwidth=' . aw
+    " Handle \u0080 to \u009F as control chars even on MS-Windows.
+    set isprint=@,161-255
+
+    call setcellwidths([])
+    " Control chars
+    call assert_equal(4, strwidth("\u0081"))
+    call assert_equal(6, strwidth("\uFEFF"))
+    " Ambiguous width chars
+    call assert_equal((aw == 'single') ? 1 : 2, strwidth("\u00A1"))
+    call assert_equal((aw == 'single') ? 1 : 2, strwidth("\u2010"))
+
+    call setcellwidths([[0x81, 0x81, 1], [0xA1, 0xA1, 1],
+                      \ [0x2010, 0x2010, 1], [0xFEFF, 0xFEFF, 1]])
+    " Control chars
+    call assert_equal(4, strwidth("\u0081"))
+    call assert_equal(6, strwidth("\uFEFF"))
+    " Ambiguous width chars
+    call assert_equal(1, strwidth("\u00A1"))
+    call assert_equal(1, strwidth("\u2010"))
+
+    call setcellwidths([[0x81, 0x81, 2], [0xA1, 0xA1, 2],
+                      \ [0x2010, 0x2010, 2], [0xFEFF, 0xFEFF, 2]])
+    " Control chars
+    call assert_equal(4, strwidth("\u0081"))
+    call assert_equal(6, strwidth("\uFEFF"))
+    " Ambiguous width chars
+    call assert_equal(2, strwidth("\u00A1"))
+    call assert_equal(2, strwidth("\u2010"))
+  endfor
+  set ambiwidth& isprint&
+
   call setcellwidths([])
 
   call assert_fails('call setcellwidths(1)', 'E1211:')