diff --git a/src/evalfunc.c b/src/evalfunc.c
index b752c51..1fad082 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -331,6 +331,18 @@
 }
 
 /*
+ * Check "type" is a bool or number 0 or 1.
+ */
+    static int
+arg_bool(type_T *type, argcontext_T *context)
+{
+    if (type->tt_type == VAR_ANY
+		   || type->tt_type == VAR_NUMBER || type->tt_type == VAR_BOOL)
+	return OK;
+    return check_arg_type(&t_bool, type, context);
+}
+
+/*
  * Check "type" is a list or a blob.
  */
     static int
@@ -423,6 +435,7 @@
 /*
  * Lists of functions that check the argument types of a builtin function.
  */
+argcheck_T arg3_string_nr_bool[] = {arg_string, arg_number, arg_bool};
 argcheck_T arg1_float_or_nr[] = {arg_float_or_nr};
 argcheck_T arg2_listblob_item[] = {arg_list_or_blob, arg_item_of_prev};
 argcheck_T arg23_extend[] = {arg_list_or_dict, arg_same_as_prev, arg_extend3};
@@ -1552,7 +1565,7 @@
 			ret_float,	    FLOAT_FUNC(f_str2float)},
     {"str2list",	1, 2, FEARG_1,	    NULL,
 			ret_list_number,    f_str2list},
-    {"str2nr",		1, 3, FEARG_1,	    NULL,
+    {"str2nr",		1, 3, FEARG_1,	    arg3_string_nr_bool,
 			ret_number,	    f_str2nr},
     {"strcharpart",	2, 3, FEARG_1,	    NULL,
 			ret_string,	    f_strcharpart},
@@ -9076,7 +9089,7 @@
 	    what |= STR2NR_QUOTE;
     }
 
-    p = skipwhite(tv_get_string(&argvars[0]));
+    p = skipwhite(tv_get_string_strict(&argvars[0]));
     isneg = (*p == '-');
     if (*p == '+' || *p == '-')
 	p = skipwhite(p + 1);
diff --git a/src/proto/typval.pro b/src/proto/typval.pro
index 7a65376..93eb64f 100644
--- a/src/proto/typval.pro
+++ b/src/proto/typval.pro
@@ -12,9 +12,11 @@
 int check_for_string(typval_T *tv);
 int check_for_nonempty_string(typval_T *tv);
 char_u *tv_get_string(typval_T *varp);
+char_u *tv_get_string_strict(typval_T *varp);
 char_u *tv_get_string_buf(typval_T *varp, char_u *buf);
 char_u *tv_get_string_chk(typval_T *varp);
 char_u *tv_get_string_buf_chk(typval_T *varp, char_u *buf);
+char_u *tv_get_string_buf_chk_strict(typval_T *varp, char_u *buf, int strict);
 char_u *tv_stringify(typval_T *varp, char_u *buf);
 int tv_check_lock(typval_T *tv, char_u *name, int use_gettext);
 void copy_tv(typval_T *from, typval_T *to);
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index 776aec0..2929100 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -867,6 +867,13 @@
 
 def Test_str2nr()
   str2nr("1'000'000", 10, true)->assert_equal(1000000)
+
+  CheckDefFailure(['echo str2nr(123)'], 'E1013:')
+  CheckScriptFailure(['vim9script', 'echo str2nr(123)'], 'E1024:')
+  CheckDefFailure(['echo str2nr("123", "x")'], 'E1013:')
+  CheckScriptFailure(['vim9script', 'echo str2nr("123", "x")'], 'E1030:')
+  CheckDefFailure(['echo str2nr("123", 10, "x")'], 'E1013:')
+  CheckScriptFailure(['vim9script', 'echo str2nr("123", 10, "x")'], 'E1135:')
 enddef
 
 def Test_strchars()
diff --git a/src/typval.c b/src/typval.c
index 7e4e63d..b3325b6 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -388,6 +388,19 @@
     return tv_get_string_buf(varp, mybuf);
 }
 
+/*
+ * Like tv_get_string() but don't allow number to string conversion for Vim9.
+ */
+    char_u *
+tv_get_string_strict(typval_T *varp)
+{
+    static char_u   mybuf[NUMBUFLEN];
+    char_u	    *res =  tv_get_string_buf_chk_strict(
+						 varp, mybuf, in_vim9script());
+
+    return res != NULL ? res : (char_u *)"";
+}
+
     char_u *
 tv_get_string_buf(typval_T *varp, char_u *buf)
 {
@@ -410,9 +423,20 @@
     char_u *
 tv_get_string_buf_chk(typval_T *varp, char_u *buf)
 {
+    return tv_get_string_buf_chk_strict(varp, buf, FALSE);
+}
+
+    char_u *
+tv_get_string_buf_chk_strict(typval_T *varp, char_u *buf, int strict)
+{
     switch (varp->v_type)
     {
 	case VAR_NUMBER:
+	    if (strict)
+	    {
+		emsg(_(e_using_number_as_string));
+		break;
+	    }
 	    vim_snprintf((char *)buf, NUMBUFLEN, "%lld",
 					    (varnumber_T)varp->vval.v_number);
 	    return buf;
diff --git a/src/version.c b/src/version.c
index 555a2f9..8159289 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2434,
+/**/
     2433,
 /**/
     2432,