diff --git a/src/buffer.c b/src/buffer.c
index 5d88d01c04..a36e3b12aa 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -595,6 +595,7 @@ close_buffer(
     if (buf->b_nwindows == 1)
     {
 	++buf->b_locked;
+	++buf->b_locked_split;
 	if (apply_autocmds(EVENT_BUFWINLEAVE, buf->b_fname, buf->b_fname,
 								  FALSE, buf)
 		&& !bufref_valid(&bufref))
@@ -605,6 +606,7 @@ aucmd_abort:
 	    return FALSE;
 	}
 	--buf->b_locked;
+	--buf->b_locked_split;
 	if (abort_if_last && one_window())
 	    // Autocommands made this the only window.
 	    goto aucmd_abort;
@@ -614,12 +616,14 @@ aucmd_abort:
 	if (!unload_buf)
 	{
 	    ++buf->b_locked;
+	    ++buf->b_locked_split;
 	    if (apply_autocmds(EVENT_BUFHIDDEN, buf->b_fname, buf->b_fname,
 								  FALSE, buf)
 		    && !bufref_valid(&bufref))
 		// Autocommands deleted the buffer.
 		goto aucmd_abort;
 	    --buf->b_locked;
+	    --buf->b_locked_split;
 	    if (abort_if_last && one_window())
 		// Autocommands made this the only window.
 		goto aucmd_abort;
@@ -804,6 +808,7 @@ buf_freeall(buf_T *buf, int flags)
 
     // Make sure the buffer isn't closed by autocommands.
     ++buf->b_locked;
+    ++buf->b_locked_split;
     set_bufref(&bufref, buf);
     if (buf->b_ml.ml_mfp != NULL)
     {
@@ -830,6 +835,7 @@ buf_freeall(buf_T *buf, int flags)
 	    return;
     }
     --buf->b_locked;
+    --buf->b_locked_split;
 
     // If the buffer was in curwin and the window has changed, go back to that
     // window, if it still exists.  This avoids that ":edit x" triggering a
@@ -1722,8 +1728,8 @@ set_curbuf(buf_T *buf, int action)
     set_bufref(&prevbufref, prevbuf);
     set_bufref(&newbufref, buf);
 
-    // Autocommands may delete the current buffer and/or the buffer we want to go
-    // to.  In those cases don't close the buffer.
+    // Autocommands may delete the current buffer and/or the buffer we want to
+    // go to.  In those cases don't close the buffer.
     if (!apply_autocmds(EVENT_BUFLEAVE, NULL, NULL, FALSE, curbuf)
 	    || (bufref_valid(&prevbufref)
 		&& bufref_valid(&newbufref)
diff --git a/src/dict.c b/src/dict.c
index 260f229850..b36b2bf6dd 100644
--- a/src/dict.c
+++ b/src/dict.c
@@ -945,7 +945,7 @@ eval_dict(char_u **arg, typval_T *rettv, evalarg_T *evalarg, int literal)
 	if (**arg != ':')
 	{
 	    if (*skipwhite(*arg) == ':')
-		semsg(_(e_no_white_space_allowed_before_str), ":");
+		semsg(_(e_no_white_space_allowed_before_str_str), ":", *arg);
 	    else
 		semsg(_(e_missing_dict_colon), *arg);
 	    clear_tv(&tvkey);
@@ -970,7 +970,7 @@ eval_dict(char_u **arg, typval_T *rettv, evalarg_T *evalarg, int literal)
 	}
 	if (vim9script && (*arg)[1] != NUL && !VIM_ISWHITE((*arg)[1]))
 	{
-	    semsg(_(e_white_space_required_after_str), ":");
+	    semsg(_(e_white_space_required_after_str_str), ":", *arg);
 	    clear_tv(&tvkey);
 	    goto failret;
 	}
@@ -1012,7 +1012,7 @@ eval_dict(char_u **arg, typval_T *rettv, evalarg_T *evalarg, int literal)
 	{
 	    if (vim9script && (*arg)[1] != NUL && !VIM_ISWHITE((*arg)[1]))
 	    {
-		semsg(_(e_white_space_required_after_str), ",");
+		semsg(_(e_white_space_required_after_str_str), ",", *arg);
 		goto failret;
 	    }
 	    *arg = skipwhite(*arg + 1);
@@ -1025,7 +1025,7 @@ eval_dict(char_u **arg, typval_T *rettv, evalarg_T *evalarg, int literal)
 	if (!had_comma)
 	{
 	    if (**arg == ',')
-		semsg(_(e_no_white_space_allowed_before_str), ",");
+		semsg(_(e_no_white_space_allowed_before_str_str), ",", *arg);
 	    else
 		semsg(_(e_missing_dict_comma), *arg);
 	    goto failret;
diff --git a/src/errors.h b/src/errors.h
index e6d7ab26c8..9b9a782753 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -173,10 +173,10 @@ EXTERN char e_cannot_declare_a_register_str[]
 	INIT(= N_("E1066: Cannot declare a register: %s"));
 EXTERN char e_separator_mismatch_str[]
 	INIT(= N_("E1067: Separator mismatch: %s"));
-EXTERN char e_no_white_space_allowed_before_str[]
-	INIT(= N_("E1068: No white space allowed before '%s'"));
-EXTERN char e_white_space_required_after_str[]
-	INIT(= N_("E1069: White space required after '%s'"));
+EXTERN char e_no_white_space_allowed_before_str_str[]
+	INIT(= N_("E1068: No white space allowed before '%s': %s"));
+EXTERN char e_white_space_required_after_str_str[]
+	INIT(= N_("E1069: White space required after '%s': %s"));
 EXTERN char e_missing_from[]
 	INIT(= N_("E1070: Missing \"from\""));
 EXTERN char e_invalid_string_after_from[]
@@ -353,3 +353,7 @@ EXTERN char e_missing_return_type[]
 	INIT(= N_("E1157: Missing return type"));
 EXTERN char e_cannot_use_flatten_in_vim9_script[]
 	INIT(= N_("E1158: Cannot use flatten() in Vim9 script"));
+EXTERN char e_cannot_split_window_when_closing_buffer[]
+	INIT(= N_("E1159: Cannot split a window when closing the buffer"));
+EXTERN char e_cannot_use_default_for_variable_arguments[]
+	INIT(= N_("E1160: Cannot use a default for variable arguments"));
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 40e5eed9d7..b5bdcd3cde 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -5218,8 +5218,7 @@ ends_excmd2(char_u *cmd_start UNUSED, char_u *cmd)
 	return TRUE;
 #ifdef FEAT_EVAL
     if (in_vim9script())
-	return c == '#' && cmd[1] != '{'
-				 && (cmd == cmd_start || VIM_ISWHITE(cmd[-1]));
+	return c == '#' && (cmd == cmd_start || VIM_ISWHITE(cmd[-1]));
 #endif
     return c == '"';
 }
diff --git a/src/filepath.c b/src/filepath.c
index b8bfc78096..99193383fe 100644
--- a/src/filepath.c
+++ b/src/filepath.c
@@ -3360,7 +3360,10 @@ dos_expandpath(
 	if (p == NULL)
 	    break;  // out of memory
 
-	if (*wfb.cAlternateFileName == NUL)
+	// Do not use the alternate filename when the file name ends in '~',
+	// because it picks up backup files: short name for "foo.vim~" is
+	// "foo~1.vim", which matches "*.vim".
+	if (*wfb.cAlternateFileName == NUL || p[STRLEN(p) - 1] == '~')
 	    p_alt = NULL;
 	else
 	    p_alt = utf16_to_enc(wfb.cAlternateFileName, NULL);
diff --git a/src/list.c b/src/list.c
index c51c99bc90..4d33aa6e08 100644
--- a/src/list.c
+++ b/src/list.c
@@ -1311,7 +1311,7 @@ eval_list(char_u **arg, typval_T *rettv, evalarg_T *evalarg, int do_error)
 	{
 	    if (vim9script && !IS_WHITE_OR_NUL((*arg)[1]) && (*arg)[1] != ']')
 	    {
-		semsg(_(e_white_space_required_after_str), ",");
+		semsg(_(e_white_space_required_after_str_str), ",", *arg);
 		goto failret;
 	    }
 	    *arg = skipwhite(*arg + 1);
@@ -1328,7 +1328,8 @@ eval_list(char_u **arg, typval_T *rettv, evalarg_T *evalarg, int do_error)
 	    if (do_error)
 	    {
 		if (**arg == ',')
-		    semsg(_(e_no_white_space_allowed_before_str), ",");
+		    semsg(_(e_no_white_space_allowed_before_str_str),
+								    ",", *arg);
 		else
 		    semsg(_("E696: Missing comma in List: %s"), *arg);
 	    }
diff --git a/src/popupwin.c b/src/popupwin.c
index 436238f9ba..47e7338b74 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -1941,7 +1941,7 @@ popup_create(typval_T *argvars, typval_T *rettv, create_type_T type)
 	buf->b_p_ul = -1;	// no undo
 	buf->b_p_swf = FALSE;   // no swap file
 	buf->b_p_bl = FALSE;    // unlisted buffer
-	buf->b_locked = TRUE;
+	buf->b_locked = TRUE;	// prevent deleting the buffer
 
 	// Avoid that 'buftype' is reset when this buffer is entered.
 	buf->b_p_initialized = TRUE;
diff --git a/src/scriptfile.c b/src/scriptfile.c
index c8a23d55a3..82ae42a1a6 100644
--- a/src/scriptfile.c
+++ b/src/scriptfile.c
@@ -1319,6 +1319,9 @@ do_source(
 	    }
 	// imports can be redefined once
 	mark_imports_for_reload(sid);
+
+	// reset version, "vim9script" may have been added or removed.
+	si->sn_version = 1;
     }
     else
     {
@@ -1457,7 +1460,7 @@ almosttheend:
     if (si->sn_save_cpo != NULL)
     {
 	set_option_value((char_u *)"cpo", 0L, si->sn_save_cpo, 0);
-	CLEAR_POINTER(si->sn_save_cpo);
+	VIM_CLEAR(si->sn_save_cpo);
     }
 
     restore_funccal();
diff --git a/src/structs.h b/src/structs.h
index d6c0b15340..9ab14fd381 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -2636,6 +2636,8 @@ struct file_buffer
     int		b_flags;	// various BF_ flags
     int		b_locked;	// Buffer is being closed or referenced, don't
 				// let autocommands wipe it out.
+    int		b_locked_split;	// Buffer is being closed, don't allow opening
+				// a new window with it.
 
     /*
      * b_ffname has the full path of the file (NULL for no name).
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index df2b9c89cf..5839691aa9 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -2761,15 +2761,15 @@ endfunc
 
 " Fuzzer found some strange combination that caused a crash.
 func Test_autocmd_normal_mess()
-  " TODO: why does this hang on Windows?
+  " For unknown reason this hangs on MS-Windows
   CheckNotMSWindows
 
   augroup aucmd_normal_test
     au BufLeave,BufWinLeave,BufHidden,BufUnload,BufDelete,BufWipeout * norm 7q/qc
   augroup END
-  o4
+  call assert_fails('o4', 'E1159')
   silent! H
-  e xx
+  call assert_fails('e xx', 'E1159')
   normal G
 
   augroup aucmd_normal_test
@@ -2778,6 +2778,9 @@ func Test_autocmd_normal_mess()
 endfunc
 
 func Test_autocmd_closing_cmdwin()
+  " For unknown reason this hangs on MS-Windows
+  CheckNotMSWindows
+
   au BufWinLeave * nested q
   call assert_fails("norm 7q?\n", 'E855:')
 
@@ -2791,8 +2794,8 @@ func Test_autocmd_vimgrep()
     au QuickfixCmdPre,BufNew,BufDelete,BufReadCmd * sb
     au QuickfixCmdPre,BufNew,BufDelete,BufReadCmd * q9
   augroup END
-  " TODO: if this is executed directly valgrind reports errors
-  call assert_fails('lv?a?', 'E926:')
+  %bwipe!
+  call assert_fails('lv ?a? foo', 'E926:')
 
   augroup aucmd_vimgrep
     au!
diff --git a/src/testdir/test_bufline.vim b/src/testdir/test_bufline.vim
index b2de198ef0..5df5288184 100644
--- a/src/testdir/test_bufline.vim
+++ b/src/testdir/test_bufline.vim
@@ -40,11 +40,13 @@ func Test_setbufline_getbufline()
   call assert_equal([], getbufline(b, 6))
   call assert_equal([], getbufline(b, 2, 1))
 
-  call setbufline(b, 2, [function('eval'), #{key: 123}, test_null_job()])
-  call assert_equal(["function('eval')",
-                  \ "{'key': 123}",
-                  \ "no process"],
-                  \ getbufline(b, 2, 4))
+  if has('job')
+    call setbufline(b, 2, [function('eval'), #{key: 123}, test_null_job()])
+    call assert_equal(["function('eval')",
+                    \ "{'key': 123}",
+                    \ "no process"],
+                    \ getbufline(b, 2, 4))
+  endif
   exe "bwipe! " . b
 endfunc
 
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index 06839c0c51..eb36bd77a1 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -824,11 +824,13 @@ def Test_set_get_bufline()
       assert_equal([], getbufline(b, 6))
       assert_equal([], getbufline(b, 2, 1))
 
-      setbufline(b, 2, [function('eval'), {key: 123}, test_null_job()])
-      assert_equal(["function('eval')",
-                      "{'key': 123}",
-                      "no process"],
-                      getbufline(b, 2, 4))
+      if has('job')
+        setbufline(b, 2, [function('eval'), {key: 123}, test_null_job()])
+        assert_equal(["function('eval')",
+                        "{'key': 123}",
+                        "no process"],
+                        getbufline(b, 2, 4))
+      endif
 
       exe 'bwipe! ' .. b
   END
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 73ff693fa9..cdaba5af74 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -781,6 +781,16 @@ def Test_call_def_varargs()
       Func(1, 'a')
   END
   CheckScriptFailure(lines, 'E1013: Argument 1: type mismatch')
+
+  lines =<< trim END
+      vim9script
+      def Func(  # some comment
+                ...l = []
+                )
+        echo l
+      enddef
+  END
+  CheckScriptFailure(lines, 'E1160:')
 enddef
 
 let s:value = ''
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index d25bb47aaa..42a0d61dd0 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -1743,6 +1743,21 @@ def Test_if_elseif_else_fails()
   CheckDefFailure(['endif'], 'E580:')
   CheckDefFailure(['if g:abool', 'elseif xxx'], 'E1001:')
   CheckDefFailure(['if true', 'echo 1'], 'E171:')
+
+  var lines =<< trim END
+      var s = ''
+      if s = ''
+      endif
+  END
+  CheckDefFailure(lines, 'E488:')
+
+  lines =<< trim END
+      var s = ''
+      if s == ''
+      elseif s = ''
+      endif
+  END
+  CheckDefFailure(lines, 'E488:')
 enddef
 
 let g:bool_true = v:true
@@ -2190,6 +2205,10 @@ def Test_while_loop()
     result ..= cnt .. '_'
   endwhile
   assert_equal('1_3_', result)
+
+  var s = ''
+  while s == 'x' #{comment}
+  endwhile
 enddef
 
 def Test_while_loop_fails()
@@ -2200,6 +2219,13 @@ def Test_while_loop_fails()
   CheckDefFailure(['break'], 'E587:')
   CheckDefFailure(['if true', 'break'], 'E587:')
   CheckDefFailure(['while 1', 'echo 3'], 'E170:')
+
+  var lines =<< trim END
+      var s = ''
+      while s = ''
+      endwhile
+  END
+  CheckDefFailure(lines, 'E488:')
 enddef
 
 def Test_interrupt_loop()
@@ -3129,6 +3155,19 @@ def Test_restoring_cpo()
   delete('Xsourced')
   delete('Xclose')
   delete('Xdone')
+
+  writefile(['vim9script'], 'XanotherScript')
+  set cpo=aABceFsMny>
+  edit XanotherScript
+  so %
+  assert_equal('aABceFsMny>', &cpo)
+  :1del
+  w
+  so %
+  assert_equal('aABceFsMny>', &cpo)
+
+  delete('XanotherScript')
+  set cpo&vim
 enddef
 
 
diff --git a/src/userfunc.c b/src/userfunc.c
index bdf4064263..c9b15fd638 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -126,7 +126,7 @@ one_function_arg(
 	    ++p;
 	    if (!skip && !VIM_ISWHITE(*p))
 	    {
-		semsg(_(e_white_space_required_after_str), ":");
+		semsg(_(e_white_space_required_after_str_str), ":", p - 1);
 		return arg;
 	    }
 	    type = skipwhite(p);
@@ -241,6 +241,11 @@ get_function_args(
 									 skip);
 		if (p == arg)
 		    break;
+		if (*skipwhite(p) == '=')
+		{
+		    emsg(_(e_cannot_use_default_for_variable_arguments));
+		    break;
+		}
 	    }
 	}
 	else
@@ -297,7 +302,7 @@ get_function_args(
 		if (!skip && in_vim9script()
 				      && !IS_WHITE_OR_NUL(*p) && *p != endchar)
 		{
-		    semsg(_(e_white_space_required_after_str), ",");
+		    semsg(_(e_white_space_required_after_str_str), ",", p - 1);
 		    goto err_ret;
 		}
 	    }
@@ -487,7 +492,7 @@ skip_arrow(
 	    if (white_error != NULL && !VIM_ISWHITE(s[1]))
 	    {
 		*white_error = TRUE;
-		semsg(_(e_white_space_required_after_str), ":");
+		semsg(_(e_white_space_required_after_str_str), ":", s);
 		return NULL;
 	    }
 	    s = skipwhite(s + 1);
@@ -873,7 +878,7 @@ get_func_tv(
 	{
 	    if (*argp != ',' && *skipwhite(argp) == ',')
 	    {
-		semsg(_(e_no_white_space_allowed_before_str), ",");
+		semsg(_(e_no_white_space_allowed_before_str_str), ",", argp);
 		ret = FAIL;
 		break;
 	    }
@@ -884,7 +889,7 @@ get_func_tv(
 	    break;
 	if (vim9script && !IS_WHITE_OR_NUL(argp[1]))
 	{
-	    semsg(_(e_white_space_required_after_str), ",");
+	    semsg(_(e_white_space_required_after_str_str), ",", argp);
 	    ret = FAIL;
 	    break;
 	}
@@ -3209,7 +3214,7 @@ define_function(exarg_T *eap, char_u *name_arg)
 
     if ((vim9script || eap->cmdidx == CMD_def) && VIM_ISWHITE(p[-1]))
     {
-	semsg(_(e_no_white_space_allowed_before_str), "(");
+	semsg(_(e_no_white_space_allowed_before_str_str), "(", p - 1);
 	goto ret_free;
     }
 
diff --git a/src/version.c b/src/version.c
index b6889cf6ff..1951e15d45 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,28 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2486,
+/**/
+    2485,
+/**/
+    2484,
+/**/
+    2483,
+/**/
+    2482,
+/**/
+    2481,
+/**/
+    2480,
+/**/
+    2479,
+/**/
+    2478,
+/**/
+    2477,
+/**/
+    2476,
 /**/
     2475,
 /**/
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 6a1d8d9e78..512f7246c2 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -2800,14 +2800,14 @@ compile_arguments(char_u **arg, cctx_T *cctx, int *argcount)
 
 	if (*p != ',' && *skipwhite(p) == ',')
 	{
-	    semsg(_(e_no_white_space_allowed_before_str), ",");
+	    semsg(_(e_no_white_space_allowed_before_str_str), ",", p);
 	    p = skipwhite(p);
 	}
 	if (*p == ',')
 	{
 	    ++p;
 	    if (*p != NUL && !VIM_ISWHITE(*p))
-		semsg(_(e_white_space_required_after_str), ",");
+		semsg(_(e_white_space_required_after_str_str), ",", p - 1);
 	}
 	else
 	    must_end = TRUE;
@@ -3055,7 +3055,7 @@ compile_list(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
 	}
 	if (*p == ',')
 	{
-	    semsg(_(e_no_white_space_allowed_before_str), ",");
+	    semsg(_(e_no_white_space_allowed_before_str_str), ",", p);
 	    return FAIL;
 	}
 	if (*p == ']')
@@ -3073,7 +3073,7 @@ compile_list(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
 	    ++p;
 	    if (*p != ']' && !IS_WHITE_OR_NUL(*p))
 	    {
-		semsg(_(e_white_space_required_after_str), ",");
+		semsg(_(e_white_space_required_after_str_str), ",", p - 1);
 		return FAIL;
 	    }
 	}
@@ -3234,7 +3234,7 @@ compile_dict(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
 	if (**arg != ':')
 	{
 	    if (*skipwhite(*arg) == ':')
-		semsg(_(e_no_white_space_allowed_before_str), ":");
+		semsg(_(e_no_white_space_allowed_before_str_str), ":", *arg);
 	    else
 		semsg(_(e_missing_dict_colon), *arg);
 	    return FAIL;
@@ -3242,7 +3242,7 @@ compile_dict(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
 	whitep = *arg + 1;
 	if (!IS_WHITE_OR_NUL(*whitep))
 	{
-	    semsg(_(e_white_space_required_after_str), ":");
+	    semsg(_(e_white_space_required_after_str_str), ":", *arg);
 	    return FAIL;
 	}
 
@@ -3273,16 +3273,16 @@ compile_dict(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
 	}
 	if (IS_WHITE_OR_NUL(*whitep))
 	{
-	    semsg(_(e_no_white_space_allowed_before_str), ",");
+	    semsg(_(e_no_white_space_allowed_before_str_str), ",", whitep);
 	    return FAIL;
 	}
 	whitep = *arg + 1;
 	if (!IS_WHITE_OR_NUL(*whitep))
 	{
-	    semsg(_(e_white_space_required_after_str), ",");
+	    semsg(_(e_white_space_required_after_str_str), ",", *arg);
 	    return FAIL;
 	}
-	*arg = skipwhite(*arg + 1);
+	*arg = skipwhite(whitep);
     }
 
     *arg = *arg + 1;
@@ -4270,7 +4270,7 @@ compile_expr7t(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
 	if (**arg != '>')
 	{
 	    if (*skipwhite(*arg) == '>')
-		semsg(_(e_no_white_space_allowed_before_str), ">");
+		semsg(_(e_no_white_space_allowed_before_str_str), ">", *arg);
 	    else
 		emsg(_(e_missing_gt));
 	    return FAIL;
@@ -5711,7 +5711,7 @@ compile_lhs(
 	    // parse optional type: "let var: type = expr"
 	    if (!VIM_ISWHITE(var_end[1]))
 	    {
-		semsg(_(e_white_space_required_after_str), ":");
+		semsg(_(e_white_space_required_after_str_str), ":", var_end);
 		return FAIL;
 	    }
 	    p = skipwhite(var_end + 1);
@@ -6701,6 +6701,11 @@ compile_if(char_u *arg, cctx_T *cctx)
 	clear_ppconst(&ppconst);
 	return NULL;
     }
+    if (!ends_excmd2(arg, skipwhite(p)))
+    {
+	semsg(_(e_trailing_arg), p);
+	return NULL;
+    }
     if (cctx->ctx_skip == SKIP_YES)
 	clear_ppconst(&ppconst);
     else if (instr->ga_len == instr_count && ppconst.pp_used == 1)
@@ -6825,6 +6830,11 @@ compile_elseif(char_u *arg, cctx_T *cctx)
 	return NULL;
     }
     cctx->ctx_skip = save_skip;
+    if (!ends_excmd2(arg, skipwhite(p)))
+    {
+	semsg(_(e_trailing_arg), p);
+	return NULL;
+    }
     if (scope->se_skip_save == SKIP_YES)
 	clear_ppconst(&ppconst);
     else if (instr->ga_len == instr_count && ppconst.pp_used == 1)
@@ -7237,6 +7247,11 @@ compile_while(char_u *arg, cctx_T *cctx)
     // compile "expr"
     if (compile_expr0(&p, cctx) == FAIL)
 	return NULL;
+    if (!ends_excmd2(arg, skipwhite(p)))
+    {
+	semsg(_(e_trailing_arg), p);
+	return NULL;
+    }
 
     if (bool_on_stack(cctx) == FAIL)
 	return FAIL;
diff --git a/src/vim9script.c b/src/vim9script.c
index 010b4bfdb3..387c9bedc4 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -629,7 +629,7 @@ vim9_declare_scriptvar(exarg_T *eap, char_u *arg)
     }
     if (!VIM_ISWHITE(p[1]))
     {
-	semsg(_(e_white_space_required_after_str), ":");
+	semsg(_(e_white_space_required_after_str_str), ":", p);
 	return arg + STRLEN(arg);
     }
     name = vim_strnsave(arg, p - arg);
diff --git a/src/vim9type.c b/src/vim9type.c
index 1374cee1b1..1a20ef5796 100644
--- a/src/vim9type.c
+++ b/src/vim9type.c
@@ -638,7 +638,7 @@ parse_type_member(
 	if (give_error)
 	{
 	    if (*skipwhite(*arg) == '<')
-		semsg(_(e_no_white_space_allowed_before_str), "<");
+		semsg(_(e_no_white_space_allowed_before_str_str), "<", *arg);
 	    else
 		emsg(_(e_missing_type));
 	}
@@ -779,7 +779,8 @@ parse_type(char_u **arg, garray_T *type_gap, int give_error)
 			if (*p != ',' && *skipwhite(p) == ',')
 			{
 			    if (give_error)
-				semsg(_(e_no_white_space_allowed_before_str), ",");
+				semsg(_(e_no_white_space_allowed_before_str_str),
+								       ",", p);
 			    return NULL;
 			}
 			if (*p == ',')
@@ -788,7 +789,8 @@ parse_type(char_u **arg, garray_T *type_gap, int give_error)
 			    if (!VIM_ISWHITE(*p))
 			    {
 				if (give_error)
-				    semsg(_(e_white_space_required_after_str), ",");
+				    semsg(_(e_white_space_required_after_str_str),
+								   ",", p - 1);
 				return NULL;
 			    }
 			}
@@ -815,7 +817,8 @@ parse_type(char_u **arg, garray_T *type_gap, int give_error)
 		    // parse return type
 		    ++*arg;
 		    if (!VIM_ISWHITE(**arg) && give_error)
-			semsg(_(e_white_space_required_after_str), ":");
+			semsg(_(e_white_space_required_after_str_str),
+								":", *arg - 1);
 		    *arg = skipwhite(*arg);
 		    ret_type = parse_type(arg, type_gap, give_error);
 		    if (ret_type == NULL)
diff --git a/src/window.c b/src/window.c
index 2c085a6480..17f36a9932 100644
--- a/src/window.c
+++ b/src/window.c
@@ -769,6 +769,11 @@ check_split_disallowed()
 	emsg(_("E242: Can't split a window while closing another"));
 	return FAIL;
     }
+    if (curwin->w_buffer->b_locked_split)
+    {
+	emsg(_(e_cannot_split_window_when_closing_buffer));
+	return FAIL;
+    }
     return OK;
 }
 
@@ -793,6 +798,9 @@ win_split(int size, int flags)
     if (ERROR_IF_ANY_POPUP_WINDOW)
 	return FAIL;
 
+    if (check_split_disallowed() == FAIL)
+	return FAIL;
+
     // When the ":tab" modifier was used open a new tab page instead.
     if (may_open_tabpage() == OK)
 	return OK;
@@ -804,8 +812,6 @@ win_split(int size, int flags)
 	emsg(_("E442: Can't split topleft and botright at the same time"));
 	return FAIL;
     }
-    if (check_split_disallowed() == FAIL)
-	return FAIL;
 
     // When creating the help window make a snapshot of the window layout.
     // Otherwise clear the snapshot, it's now invalid.