diff --git a/src/nvim/optionstr.c b/src/nvim/optionstr.c
index 307c4ae79f..48423a1779 100644
--- a/src/nvim/optionstr.c
+++ b/src/nvim/optionstr.c
@@ -655,6 +655,9 @@ const char *did_set_backupcopy(optset_T *args)
   if (opt_flags & OPT_LOCAL) {
     bkc = buf->b_p_bkc;
     flags = &buf->b_bkc_flags;
+  } else if (!(opt_flags & OPT_GLOBAL)) {
+    // When using :set, clear the local flags.
+    buf->b_bkc_flags = 0;
   }
 
   if ((opt_flags & OPT_LOCAL) && *bkc == NUL) {
@@ -1070,6 +1073,9 @@ const char *did_set_completeopt(optset_T *args FUNC_ATTR_UNUSED)
   if (args->os_flags & OPT_LOCAL) {
     cot = buf->b_p_cot;
     flags = &buf->b_cot_flags;
+  } else if (!(args->os_flags & OPT_GLOBAL)) {
+    // When using :set, clear the local flags.
+    buf->b_cot_flags = 0;
   }
 
   if (check_opt_strings(cot, p_cot_values, true) != OK) {
diff --git a/test/old/testdir/test_ins_complete.vim b/test/old/testdir/test_ins_complete.vim
index 8e2a7c4631..01695d5be5 100644
--- a/test/old/testdir/test_ins_complete.vim
+++ b/test/old/testdir/test_ins_complete.vim
@@ -950,6 +950,46 @@ func Test_completeopt_buffer_local()
   call assert_equal('menu', &completeopt)
   call assert_equal('menu', &g:completeopt)
 
+  new | only
+  call setline(1, ['foofoo', 'foobar', 'foobaz', ''])
+  set completeopt&
+  setlocal completeopt=menu,fuzzy,noinsert
+  setglobal completeopt=menu,longest
+  call assert_equal('menu,fuzzy,noinsert', &completeopt)
+  call assert_equal('menu,fuzzy,noinsert', &l:completeopt)
+  call assert_equal('menu,longest', &g:completeopt)
+  call feedkeys("Gccf\<C-X>\<C-N>bz\<C-Y>", 'tnix')
+  call assert_equal('foobaz', getline('.'))
+  setlocal bufhidden=wipe
+  new | only!
+  call setline(1, ['foofoo', 'foobar', 'foobaz', ''])
+  call assert_equal('menu,longest', &completeopt)
+  call assert_equal('menu,longest', &g:completeopt)
+  call assert_equal('', &l:completeopt)
+  call feedkeys("Gccf\<C-X>\<C-N>\<C-X>\<C-Z>", 'tnix')
+  call assert_equal('foo', getline('.'))
+  bwipe!
+
+  new | only
+  call setline(1, ['foofoo', 'foobar', 'foobaz', ''])
+  set completeopt&
+  setlocal completeopt=menu,fuzzy,noinsert
+  set completeopt=menu,longest
+  call assert_equal('menu,longest', &completeopt)
+  call assert_equal('menu,longest', &g:completeopt)
+  call assert_equal('', &l:completeopt)
+  call feedkeys("Gccf\<C-X>\<C-N>\<C-X>\<C-Z>", 'tnix')
+  call assert_equal('foo', getline('.'))
+  setlocal bufhidden=wipe
+  new | only!
+  call setline(1, ['foofoo', 'foobar', 'foobaz', ''])
+  call assert_equal('menu,longest', &completeopt)
+  call assert_equal('menu,longest', &g:completeopt)
+  call assert_equal('', &l:completeopt)
+  call feedkeys("Gccf\<C-X>\<C-N>\<C-X>\<C-Z>", 'tnix')
+  call assert_equal('foo', getline('.'))
+  bwipe!
+
   set completeopt&
 endfunc