diff --git a/src/edit.c b/src/edit.c
index 3f0803f..05518ce 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -175,16 +175,10 @@
 #endif
     // Don't allow changes in the buffer while editing the cmdline.  The
     // caller of getcmdline() may get confused.
-    if (textlock != 0)
-    {
-	emsg(_(e_secure));
-	return FALSE;
-    }
-
     // Don't allow recursive insert mode when busy with completion.
-    if (ins_compl_active() || compl_busy || pum_visible())
+    if (textlock != 0 || ins_compl_active() || compl_busy || pum_visible())
     {
-	emsg(_(e_secure));
+	emsg(_(e_textlock));
 	return FALSE;
     }
     ins_compl_clear();	    // clear stuff for CTRL-X mode
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 9b959fb..18da926 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -2576,7 +2576,7 @@
     if (cmdwin_type != 0)
 	return e_cmdwin;
 #endif
-    return e_secure;
+    return e_textlock;
 }
 
 /*
diff --git a/src/globals.h b/src/globals.h
index 4822bf3..f6c9d60 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -1678,9 +1678,10 @@
 EXTERN char e_readerrf[]	INIT(= N_("E47: Error while reading errorfile"));
 #endif
 #ifdef HAVE_SANDBOX
-EXTERN char e_sandbox[]	INIT(= N_("E48: Not allowed in sandbox"));
+EXTERN char e_sandbox[]		INIT(= N_("E48: Not allowed in sandbox"));
 #endif
-EXTERN char e_secure[]	INIT(= N_("E523: Not allowed here"));
+EXTERN char e_secure[]		INIT(= N_("E523: Not allowed here"));
+EXTERN char e_textlock[]	INIT(= N_("E565: Not allowed to change text here"));
 #if defined(AMIGA) || defined(MACOS_X) || defined(MSWIN)  \
 	|| defined(UNIX) || defined(VMS)
 EXTERN char e_screenmode[]	INIT(= N_("E359: Screen mode setting not supported"));
diff --git a/src/insexpand.c b/src/insexpand.c
index 0278522..48ab260 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -2217,6 +2217,8 @@
     pos = curwin->w_cursor;
     curwin_save = curwin;
     curbuf_save = curbuf;
+    // Lock the text to avoid weird things from happening.
+    ++textlock;
 
     // Call a function, which returns a list or dict.
     if (call_vim_function(funcname, 2, args, &rettv) == OK)
@@ -2239,6 +2241,7 @@
 		break;
 	}
     }
+    --textlock;
 
     if (curwin_save != curwin || curbuf_save != curbuf)
     {
@@ -2431,6 +2434,7 @@
 f_complete(typval_T *argvars, typval_T *rettv UNUSED)
 {
     int	    startcol;
+    int	    save_textlock = textlock;
 
     if ((State & INSERT) == 0)
     {
@@ -2438,22 +2442,24 @@
 	return;
     }
 
+    // "textlock" is set when evaluating 'completefunc' but we can change text
+    // here.
+    textlock = 0;
+
     // Check for undo allowed here, because if something was already inserted
     // the line was already saved for undo and this check isn't done.
     if (!undo_allowed())
 	return;
 
     if (argvars[1].v_type != VAR_LIST || argvars[1].vval.v_list == NULL)
-    {
 	emsg(_(e_invarg));
-	return;
+    else
+    {
+	startcol = (int)tv_get_number_chk(&argvars[0], NULL);
+	if (startcol > 0)
+	    set_completion(startcol - 1, argvars[1].vval.v_list);
     }
-
-    startcol = (int)tv_get_number_chk(&argvars[0], NULL);
-    if (startcol <= 0)
-	return;
-
-    set_completion(startcol - 1, argvars[1].vval.v_list);
+    textlock = save_textlock;
 }
 
 /*
diff --git a/src/testdir/test_edit.vim b/src/testdir/test_edit.vim
index 9096fcd..ce55f6b 100644
--- a/src/testdir/test_edit.vim
+++ b/src/testdir/test_edit.vim
@@ -915,6 +915,23 @@
   bw!
 endfunc
 
+func Test_edit_completefunc_delete()
+  func CompleteFunc(findstart, base)
+    if a:findstart == 1
+      return col('.') - 1
+    endif
+    normal dd
+    return ['a', 'b']
+  endfunc
+  new
+  set completefunc=CompleteFunc
+  call setline(1, ['', 'abcd', ''])
+  2d
+  call assert_fails("normal 2G$a\<C-X>\<C-U>", 'E565:')
+  bwipe!
+endfunc
+
+
 func Test_edit_CTRL_Z()
   " Ctrl-Z when insertmode is not set inserts it literally
   new
@@ -1240,7 +1257,7 @@
   try
     call feedkeys("ix\<esc>", 'tnix')
     call assert_fails(1, 'textlock')
-  catch /^Vim\%((\a\+)\)\=:E523/ " catch E523: not allowed here
+  catch /^Vim\%((\a\+)\)\=:E565/ " catch E565: not allowed here
   endtry
   " TODO: Might be a bug: should x really be inserted here
   call assert_equal(['xa'], getline(1, '$'))
@@ -1264,7 +1281,7 @@
   try
     call feedkeys("i\<c-x>\<c-u>\<esc>", 'tnix')
     call assert_fails(1, 'change in complete function')
-  catch /^Vim\%((\a\+)\)\=:E523/ " catch E523
+  catch /^Vim\%((\a\+)\)\=:E565/ " catch E565
   endtry
   delfu Complete
   set completefunc=
diff --git a/src/testdir/test_ex_mode.vim b/src/testdir/test_ex_mode.vim
index 9f66e3f..d23e0ad 100644
--- a/src/testdir/test_ex_mode.vim
+++ b/src/testdir/test_ex_mode.vim
@@ -158,13 +158,13 @@
 func Test_ex_mode_errors()
   " Not allowed to enter ex mode when text is locked
   au InsertCharPre <buffer> normal! gQ<CR>
-  let caught_e523 = 0
+  let caught_e565 = 0
   try
     call feedkeys("ix\<esc>", 'xt')
-  catch /^Vim\%((\a\+)\)\=:E523/ " catch E523
-    let caught_e523 = 1
+  catch /^Vim\%((\a\+)\)\=:E565/ " catch E565
+    let caught_e565 = 1
   endtry
-  call assert_equal(1, caught_e523)
+  call assert_equal(1, caught_e565)
   au! InsertCharPre
 endfunc
 
diff --git a/src/testdir/test_excmd.vim b/src/testdir/test_excmd.vim
index 9369c1b..868ac6f 100644
--- a/src/testdir/test_excmd.vim
+++ b/src/testdir/test_excmd.vim
@@ -354,15 +354,15 @@
 func Test_run_excmd_with_text_locked()
   " :quit
   let cmd = ":\<C-\>eexecute('quit')\<CR>\<C-C>"
-  call assert_fails("call feedkeys(cmd, 'xt')", 'E523:')
+  call assert_fails("call feedkeys(cmd, 'xt')", 'E565:')
 
   " :qall
   let cmd = ":\<C-\>eexecute('qall')\<CR>\<C-C>"
-  call assert_fails("call feedkeys(cmd, 'xt')", 'E523:')
+  call assert_fails("call feedkeys(cmd, 'xt')", 'E565:')
 
   " :exit
   let cmd = ":\<C-\>eexecute('exit')\<CR>\<C-C>"
-  call assert_fails("call feedkeys(cmd, 'xt')", 'E523:')
+  call assert_fails("call feedkeys(cmd, 'xt')", 'E565:')
 
   " :close - should be ignored
   new
@@ -370,7 +370,7 @@
   call assert_equal(2, winnr('$'))
   close
 
-  call assert_fails("call feedkeys(\":\<C-R>=execute('bnext')\<CR>\", 'xt')", 'E523:')
+  call assert_fails("call feedkeys(\":\<C-R>=execute('bnext')\<CR>\", 'xt')", 'E565:')
 endfunc
 
 " Test for the :verbose command
diff --git a/src/testdir/test_gf.vim b/src/testdir/test_gf.vim
index 829b7c2..736a315 100644
--- a/src/testdir/test_gf.vim
+++ b/src/testdir/test_gf.vim
@@ -134,13 +134,13 @@
 
   " gf is not allowed when text is locked
   au InsertCharPre <buffer> normal! gF<CR>
-  let caught_e523 = 0
+  let caught_e565 = 0
   try
     call feedkeys("ix\<esc>", 'xt')
-  catch /^Vim\%((\a\+)\)\=:E523/ " catch E523
-    let caught_e523 = 1
+  catch /^Vim\%((\a\+)\)\=:E565/ " catch E565
+    let caught_e565 = 1
   endtry
-  call assert_equal(1, caught_e523)
+  call assert_equal(1, caught_e565)
   au! InsertCharPre
 
   bwipe!
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index e96d5fd..9890377 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -334,19 +334,17 @@
   endif
 endfunc
 
-" Test that nothing happens if the 'completefunc' opens
-" a new window (no completion, no crash)
+" Test that nothing happens if the 'completefunc' tries to open
+" a new window (fails to open window, continues)
 func Test_completefunc_opens_new_window_one()
   new
   let winid = win_getid()
   setlocal completefunc=DummyCompleteOne
   call setline(1, 'one')
   /^one
-  call assert_fails('call feedkeys("A\<C-X>\<C-U>\<C-N>\<Esc>", "x")', 'E839:')
-  call assert_notequal(winid, win_getid())
-  q!
+  call assert_fails('call feedkeys("A\<C-X>\<C-U>\<C-N>\<Esc>", "x")', 'E565:')
   call assert_equal(winid, win_getid())
-  call assert_equal('', getline(1))
+  call assert_equal('oneDEF', getline(1))
   q!
 endfunc
 
diff --git a/src/undo.c b/src/undo.c
index c5ce306..c11b048 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -333,7 +333,7 @@
     // caller of getcmdline() may get confused.
     if (textlock != 0)
     {
-	emsg(_(e_secure));
+	emsg(_(e_textlock));
 	return FALSE;
     }
 
diff --git a/src/version.c b/src/version.c
index 9b00c49..cb846f0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    614,
+/**/
     613,
 /**/
     612,