diff --git a/src/dict.c b/src/dict.c
index 01a2eda..73190c4 100644
--- a/src/dict.c
+++ b/src/dict.c
@@ -862,7 +862,7 @@
 	    if (evaluate)
 	    {
 		if (*skipwhite(*arg) == ':')
-		    semsg(_(e_no_white_space_allowed_before), ":");
+		    semsg(_(e_no_white_space_allowed_before_str), ":");
 		else
 		    semsg(_(e_missing_dict_colon), *arg);
 	    }
@@ -881,7 +881,7 @@
 	}
 	if (vim9script && (*arg)[1] != NUL && !VIM_ISWHITE((*arg)[1]))
 	{
-	    semsg(_(e_white_space_required_after), ":");
+	    semsg(_(e_white_space_required_after_str), ":");
 	    clear_tv(&tvkey);
 	    goto failret;
 	}
@@ -924,7 +924,7 @@
 	{
 	    if (vim9script && (*arg)[1] != NUL && !VIM_ISWHITE((*arg)[1]))
 	    {
-		semsg(_(e_white_space_required_after), ",");
+		semsg(_(e_white_space_required_after_str), ",");
 		goto failret;
 	    }
 	    *arg = skipwhite(*arg + 1);
@@ -939,7 +939,7 @@
 	    if (evaluate)
 	    {
 		if (**arg == ',')
-		    semsg(_(e_no_white_space_allowed_before), ",");
+		    semsg(_(e_no_white_space_allowed_before_str), ",");
 		else
 		    semsg(_(e_missing_dict_comma), *arg);
 	    }
diff --git a/src/errors.h b/src/errors.h
index 60be6c1..a49aa73 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -33,7 +33,7 @@
 	INIT(= N_("E1002: Syntax error at %s"));
 EXTERN char e_missing_return_value[]
 	INIT(= N_("E1003: Missing return value"));
-EXTERN char e_white_space_required_before_and_after[]
+EXTERN char e_white_space_required_before_and_after_str[]
 	INIT(= N_("E1004: white space required before and after '%s'"));
 EXTERN char e_too_many_argument_types[]
 	INIT(= N_("E1005: Too many argument types"));
@@ -156,13 +156,13 @@
 	INIT(= N_("E1063: type mismatch for v: variable"));
 // E1064 unused
 // E1065 unused
-EXTERN char e_cannot_declare_a_register[]
+EXTERN char e_cannot_declare_a_register_str[]
 	INIT(= N_("E1066: Cannot declare a register: %s"));
-EXTERN char e_separator_mismatch[]
+EXTERN char e_separator_mismatch_str[]
 	INIT(= N_("E1067: Separator mismatch: %s"));
-EXTERN char e_no_white_space_allowed_before[]
+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[]
+EXTERN char e_white_space_required_after_str[]
 	INIT(= N_("E1069: white space required after '%s'"));
 EXTERN char e_missing_from[]
 	INIT(= N_("E1070: Missing \"from\""));
@@ -170,7 +170,7 @@
 	INIT(= N_("E1071: Invalid string after \"from\""));
 EXTERN char e_cannot_compare_str_with_str[]
 	INIT(= N_("E1072: Cannot compare %s with %s"));
-EXTERN char e_name_already_defined[]
+EXTERN char e_name_already_defined_str[]
 	INIT(= N_("E1073: name already defined: %s"));
 EXTERN char e_no_white_space_allowed_after_dot[]
 	INIT(= N_("E1074: no white space allowed after dot"));
diff --git a/src/evalvars.c b/src/evalvars.c
index 335f850..fbf521e 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -811,7 +811,7 @@
 						   || !IS_WHITE_OR_NUL(*expr)))
 	    {
 		vim_strncpy(op, expr - len, len);
-		semsg(_(e_white_space_required_before_and_after), op);
+		semsg(_(e_white_space_required_before_and_after_str), op);
 		i = FAIL;
 	    }
 
diff --git a/src/list.c b/src/list.c
index c730b1a..e7d288a 100644
--- a/src/list.c
+++ b/src/list.c
@@ -1259,7 +1259,7 @@
 	{
 	    if (vim9script && !IS_WHITE_OR_NUL((*arg)[1]))
 	    {
-		semsg(_(e_white_space_required_after), ",");
+		semsg(_(e_white_space_required_after_str), ",");
 		goto failret;
 	    }
 	    *arg = skipwhite(*arg + 1);
@@ -1276,7 +1276,7 @@
 	    if (do_error)
 	    {
 		if (**arg == ',')
-		    semsg(_(e_no_white_space_allowed_before), ",");
+		    semsg(_(e_no_white_space_allowed_before_str), ",");
 		else
 		    semsg(_("E696: Missing comma in List: %s"), *arg);
 	    }
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index 911f4ea..d9e823a 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -2336,7 +2336,8 @@
   call CheckDefFailure(["let x = '1'isnot2"], 'E488:', 1)
 
   call CheckDefFailure(["CallMe ('yes')"], 'E476:', 1)
-  call CheckDefFailure(["CallMe2('yes','no')"], 'E1069:', 1)
+  call CheckScriptFailure(["CallMe ('yes')"], 'E492:', 1)
+  call CheckScriptAndDefFailure(["CallMe2('yes','no')"], 'E1069:', 1)
   call CheckDefFailure(["CallMe2('yes' , 'no')"], 'E1068:', 1)
 
   call CheckDefFailure(["v:nosuch += 3"], 'E1001:', 1)
diff --git a/src/testdir/vim9.vim b/src/testdir/vim9.vim
index 823a6ca..2f92cf9 100644
--- a/src/testdir/vim9.vim
+++ b/src/testdir/vim9.vim
@@ -40,3 +40,10 @@
   so Xdef
   delete('Xdef')
 enddef
+
+" Check that a command fails both when used in a :def function and when used
+" in Vim9 script.
+def CheckScriptAndDefFailure(lines: list<string>, error: string, lnum = -3)
+  CheckDefFailure(lines, error, lnum)
+  CheckScriptFailure(['vim9script'] + lines, error, lnum + 1)
+enddef
diff --git a/src/userfunc.c b/src/userfunc.c
index 0f6388d..f3c04b2 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -119,7 +119,7 @@
 	    ++p;
 	    if (!VIM_ISWHITE(*p))
 	    {
-		semsg(_(e_white_space_required_after), ":");
+		semsg(_(e_white_space_required_after_str), ":");
 		return arg;
 	    }
 	    type = skipwhite(p);
@@ -276,7 +276,7 @@
 		if (!skip && in_vim9script()
 				      && !IS_WHITE_OR_NUL(*p) && *p != endchar)
 		{
-		    semsg(_(e_white_space_required_after), ",");
+		    semsg(_(e_white_space_required_after_str), ",");
 		    goto err_ret;
 		}
 	    }
@@ -623,6 +623,7 @@
     int		ret = OK;
     typval_T	argvars[MAX_FUNC_ARGS + 1];	// vars for arguments
     int		argcount = 0;		// number of arguments found
+    int		vim9script = in_vim9script();
 
     /*
      * Get the arguments.
@@ -644,10 +645,25 @@
 	++argcount;
 	// The comma should come right after the argument, but this wasn't
 	// checked previously, thus only enforce it in Vim9 script.
-	if (!in_vim9script())
+	if (vim9script)
+	{
+	    if (*argp != ',' && *skipwhite(argp) == ',')
+	    {
+		semsg(_(e_no_white_space_allowed_before_str), ",");
+		ret = FAIL;
+		break;
+	    }
+	}
+	else
 	    argp = skipwhite(argp);
 	if (*argp != ',')
 	    break;
+	if (vim9script && !IS_WHITE_OR_NUL(argp[1]))
+	{
+	    semsg(_(e_white_space_required_after_str), ",");
+	    ret = FAIL;
+	    break;
+	}
     }
     argp = skipwhite_and_linebreak(argp, evalarg);
     if (*argp == ')')
@@ -3275,7 +3291,7 @@
 			  || fp->uf_script_ctx.sc_seq == current_sctx.sc_seq)))
 	    {
 		if (vim9script)
-		    emsg_funcname(e_name_already_defined, name);
+		    emsg_funcname(e_name_already_defined_str, name);
 		else
 		    emsg_funcname(e_funcexts, name);
 		goto erret;
diff --git a/src/version.c b/src/version.c
index fe2a7ad..6773a88 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1504,
+/**/
     1503,
 /**/
     1502,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index b9d8caa..a552c85 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -295,7 +295,7 @@
 	    || find_func_even_dead(p, FALSE, cctx) != NULL)
     {
 	p[len] = c;
-	semsg(_(e_name_already_defined), p);
+	semsg(_(e_name_already_defined_str), p);
 	return FAIL;
     }
     p[len] = c;
@@ -2202,14 +2202,14 @@
 
 	if (*p != ',' && *skipwhite(p) == ',')
 	{
-	    semsg(_(e_no_white_space_allowed_before), ",");
+	    semsg(_(e_no_white_space_allowed_before_str), ",");
 	    p = skipwhite(p);
 	}
 	if (*p == ',')
 	{
 	    ++p;
 	    if (*p != NUL && !VIM_ISWHITE(*p))
-		semsg(_(e_white_space_required_after), ",");
+		semsg(_(e_white_space_required_after_str), ",");
 	}
 	whitep = p;
 	p = skipwhite(p);
@@ -2416,7 +2416,7 @@
 	}
 	if (*p == ',')
 	{
-	    semsg(_(e_no_white_space_allowed_before), ",");
+	    semsg(_(e_no_white_space_allowed_before_str), ",");
 	    return FAIL;
 	}
 	if (*p == ']')
@@ -2432,7 +2432,7 @@
 	    ++p;
 	    if (*p != ']' && !IS_WHITE_OR_NUL(*p))
 	    {
-		semsg(_(e_white_space_required_after), ",");
+		semsg(_(e_white_space_required_after_str), ",");
 		return FAIL;
 	    }
 	}
@@ -2618,7 +2618,7 @@
 	if (**arg != ':')
 	{
 	    if (*skipwhite(*arg) == ':')
-		semsg(_(e_no_white_space_allowed_before), ":");
+		semsg(_(e_no_white_space_allowed_before_str), ":");
 	    else
 		semsg(_(e_missing_dict_colon), *arg);
 	    return FAIL;
@@ -2626,7 +2626,7 @@
 	whitep = *arg + 1;
 	if (!IS_WHITE_OR_NUL(*whitep))
 	{
-	    semsg(_(e_white_space_required_after), ":");
+	    semsg(_(e_white_space_required_after_str), ":");
 	    return FAIL;
 	}
 
@@ -2657,7 +2657,7 @@
 	}
 	if (IS_WHITE_OR_NUL(*whitep))
 	{
-	    semsg(_(e_no_white_space_allowed_before), ",");
+	    semsg(_(e_no_white_space_allowed_before_str), ",");
 	    return FAIL;
 	}
 	whitep = *arg + 1;
@@ -3518,7 +3518,7 @@
     char_u	buf[10];
 
     vim_strncpy(buf, op, len);
-    semsg(_(e_white_space_required_before_and_after), buf);
+    semsg(_(e_white_space_required_before_and_after_str), buf);
 }
 
 /*
@@ -3542,7 +3542,7 @@
 	if (**arg != '>')
 	{
 	    if (*skipwhite(*arg) == '>')
-		semsg(_(e_no_white_space_allowed_before), ">");
+		semsg(_(e_no_white_space_allowed_before_str), ">");
 	    else
 		emsg(_(e_missing_gt));
 	    return FAIL;
@@ -3887,7 +3887,7 @@
 
 	    if (!IS_WHITE_OR_NUL(**arg) || !IS_WHITE_OR_NUL(p[2]))
 	    {
-		semsg(_(e_white_space_required_before_and_after), op);
+		semsg(_(e_white_space_required_before_and_after_str), op);
 		return FAIL;
 	    }
 
@@ -4028,7 +4028,7 @@
 
 	if (!IS_WHITE_OR_NUL(**arg) || !IS_WHITE_OR_NUL(p[1]))
 	{
-	    semsg(_(e_white_space_required_before_and_after), "?");
+	    semsg(_(e_white_space_required_before_and_after_str), "?");
 	    return FAIL;
 	}
 
@@ -4087,7 +4087,7 @@
 
 	if (!IS_WHITE_OR_NUL(**arg) || !IS_WHITE_OR_NUL(p[1]))
 	{
-	    semsg(_(e_white_space_required_before_and_after), ":");
+	    semsg(_(e_white_space_required_before_and_after_str), ":");
 	    return FAIL;
 	}
 
@@ -4394,7 +4394,7 @@
 		  return;
 	case '&': semsg(_(e_cannot_declare_an_option), name);
 		  return;
-	case '@': semsg(_(e_cannot_declare_a_register), name);
+	case '@': semsg(_(e_cannot_declare_a_register_str), name);
 		  return;
 	default: return;
     }
@@ -4775,7 +4775,7 @@
 		// parse optional type: "let var: type = expr"
 		if (!VIM_ISWHITE(p[1]))
 		{
-		    semsg(_(e_white_space_required_after), ":");
+		    semsg(_(e_white_space_required_after_str), ":");
 		    goto theend;
 		}
 		p = skipwhite(p + 1);
@@ -6042,7 +6042,7 @@
 	end = skip_regexp_ex(p + 1, *p, TRUE, &tofree, &dropped);
 	if (*end != *p)
 	{
-	    semsg(_(e_separator_mismatch), p);
+	    semsg(_(e_separator_mismatch_str), p);
 	    vim_free(tofree);
 	    return FAIL;
 	}
diff --git a/src/vim9script.c b/src/vim9script.c
index b9dc5d7..e86150a 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -532,7 +532,7 @@
     }
     if (!VIM_ISWHITE(p[1]))
     {
-	semsg(_(e_white_space_required_after), ":");
+	semsg(_(e_white_space_required_after_str), ":");
 	return arg + STRLEN(arg);
     }
     name = vim_strnsave(arg, p - arg);
diff --git a/src/vim9type.c b/src/vim9type.c
index 1a9b5c2..07a087b 100644
--- a/src/vim9type.c
+++ b/src/vim9type.c
@@ -471,7 +471,7 @@
     if (**arg != '<')
     {
 	if (*skipwhite(*arg) == '<')
-	    semsg(_(e_no_white_space_allowed_before), "<");
+	    semsg(_(e_no_white_space_allowed_before_str), "<");
 	else
 	    emsg(_(e_missing_type));
 	return type;
@@ -600,7 +600,7 @@
 
 			if (*p != ',' && *skipwhite(p) == ',')
 			{
-			    semsg(_(e_no_white_space_allowed_before), ",");
+			    semsg(_(e_no_white_space_allowed_before_str), ",");
 			    return &t_any;
 			}
 			if (*p == ',')
@@ -608,7 +608,7 @@
 			    ++p;
 			    if (!VIM_ISWHITE(*p))
 			    {
-				semsg(_(e_white_space_required_after), ",");
+				semsg(_(e_white_space_required_after_str), ",");
 				return &t_any;
 			    }
 			}
@@ -633,7 +633,7 @@
 		    // parse return type
 		    ++*arg;
 		    if (!VIM_ISWHITE(**arg))
-			semsg(_(e_white_space_required_after), ":");
+			semsg(_(e_white_space_required_after_str), ":");
 		    *arg = skipwhite(*arg);
 		    ret_type = parse_type(arg, type_gap);
 		}