diff --git a/src/errors.h b/src/errors.h
index 2ca71f1..3fd8e5a 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -843,4 +843,8 @@
 EXTERN char e_argument_of_str_must_be_list_string_dictionary_or_blob[]
 	INIT(= N_("E1250: Argument of %s must be a List, String, Dictionary or Blob"));
 EXTERN char e_list_dict_blob_or_string_required_for_argument_nr[]
-	INIT(= N_("E1228: List, Dictionary, Blob or String required for argument %d"));
+	INIT(= N_("E1251: List, Dictionary, Blob or String required for argument %d"));
+EXTERN char e_string_list_or_blob_required_for_argument_nr[]
+	INIT(= N_("E1252: String, List or Blob required for argument %d"));
+EXTERN char e_string_expected_for_argument_nr[]
+	INIT(= N_("E1253: String expected for argument %d"));
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 12236f7..e670381 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -465,6 +465,21 @@
 }
 
 /*
+ * Check "type" is a list of 'any' or a blob or a string.
+ */
+    static int
+arg_string_list_or_blob(type_T *type, argcontext_T *context)
+{
+    if (type->tt_type == VAR_ANY
+		     || type->tt_type == VAR_LIST
+		     || type->tt_type == VAR_BLOB
+		     || type->tt_type == VAR_STRING)
+	return OK;
+    arg_type_mismatch(&t_list_any, type, context->arg_idx + 1);
+    return FAIL;
+}
+
+/*
  * Check "type" is a job.
  */
     static int
@@ -817,7 +832,7 @@
 static argcheck_T arg25_matchadd[] = {arg_string, arg_string, arg_number, arg_number, arg_dict_any};
 static argcheck_T arg25_matchaddpos[] = {arg_string, arg_list_any, arg_number, arg_number, arg_dict_any};
 static argcheck_T arg119_printf[] = {arg_string_or_nr, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL};
-static argcheck_T arg23_reduce[] = {arg_list_or_blob, NULL, NULL};
+static argcheck_T arg23_reduce[] = {arg_string_list_or_blob, NULL, NULL};
 static argcheck_T arg24_remote_expr[] = {arg_string, arg_string, arg_string, arg_number};
 static argcheck_T arg23_remove[] = {arg_list_or_dict_or_blob, arg_remove2, arg_number};
 static argcheck_T arg2_repeat[] = {arg_repeat1, arg_number};
diff --git a/src/list.c b/src/list.c
index fafe465..484be83 100644
--- a/src/list.c
+++ b/src/list.c
@@ -314,6 +314,28 @@
 }
 
 /*
+ * Make a typval_T of the first character of "input" and store it in "output".
+ * Return OK or FAIL.
+ */
+    static int
+tv_get_first_char(char_u *input, typval_T *output)
+{
+    char_u	buf[MB_MAXBYTES + 1];
+    int		len;
+
+    if (input == NULL || output == NULL)
+	return FAIL;
+
+    len = has_mbyte ? mb_ptr2len(input) : 1;
+    STRNCPY(buf, input, len);
+    buf[len] = NUL;
+    output->v_type = VAR_STRING;
+    output->vval.v_string = vim_strsave(buf);
+
+    return output->vval.v_string == NULL ? FAIL : OK;
+}
+
+/*
  * Free a list item, unless it was allocated together with the list itself.
  * Does not clear the value.  Does not notify watchers.
  */
@@ -2492,7 +2514,6 @@
 	    char_u	*p;
 	    typval_T	tv;
 	    garray_T	ga;
-	    char_u	buf[MB_MAXBYTES + 1];
 	    int		len;
 
 	    // set_vim_var_nr() doesn't set the type
@@ -2503,16 +2524,9 @@
 	    {
 	        typval_T newtv;
 
-		if (has_mbyte)
-		    len = mb_ptr2len(p);
-		else
-		    len = 1;
-
-		STRNCPY(buf, p, len);
-		buf[len] = NUL;
-
-		tv.v_type = VAR_STRING;
-		tv.vval.v_string = vim_strsave(buf);
+		if (tv_get_first_char(p, &tv) == FAIL)
+		    break;
+		len = STRLEN(tv.vval.v_string);
 
 		set_vim_var_nr(VV_KEY, idx);
 		if (filter_map_one(&tv, expr, filtermap, &newtv, &rem) == FAIL
@@ -3248,12 +3262,17 @@
     partial_T   *partial = NULL;
     funcexe_T	funcexe;
     typval_T	argv[3];
+    int		r;
+    int		called_emsg_start = called_emsg;
 
-    if (argvars[0].v_type != VAR_LIST && argvars[0].v_type != VAR_BLOB)
-    {
-	emsg(_(e_listblobreq));
+    if (in_vim9script()
+		   && check_for_string_or_list_or_blob_arg(argvars, 0) == FAIL)
 	return;
-    }
+
+    if (argvars[0].v_type != VAR_STRING
+	    && argvars[0].v_type != VAR_LIST
+	    && argvars[0].v_type != VAR_BLOB)
+	semsg(_(e_string_list_or_blob_required), "reduce()");
 
     if (argvars[1].v_type == VAR_FUNC)
 	func_name = argvars[1].vval.v_string;
@@ -3278,8 +3297,6 @@
     {
 	list_T	    *l = argvars[0].vval.v_list;
 	listitem_T  *li = NULL;
-	int	    r;
-	int	    called_emsg_start = called_emsg;
 
 	if (l != NULL)
 	    CHECK_LIST_MATERIALIZE(l);
@@ -3319,6 +3336,43 @@
 	    l->lv_lock = prev_locked;
 	}
     }
+    else if (argvars[0].v_type == VAR_STRING)
+    {
+	char_u	*p = tv_get_string(&argvars[0]);
+	int     len;
+
+	if (argvars[2].v_type == VAR_UNKNOWN)
+	{
+	    if (*p == NUL)
+	    {
+		semsg(_(e_reduceempty), "String");
+		return;
+	    }
+	    if (tv_get_first_char(p, rettv) == FAIL)
+		return;
+	    p += STRLEN(rettv->vval.v_string);
+	}
+	else if (argvars[2].v_type != VAR_STRING)
+	{
+	    semsg(_(e_string_expected_for_argument_nr), 3);
+	    return;
+	}
+	else
+	    copy_tv(&argvars[2], rettv);
+
+	for ( ; *p != NUL; p += len)
+	{
+	    argv[0] = *rettv;
+	    if (tv_get_first_char(p, &argv[1]) == FAIL)
+		break;
+	    len = STRLEN(argv[1].vval.v_string);
+	    r = call_func(func_name, -1, rettv, 2, argv, &funcexe);
+	    clear_tv(&argv[0]);
+	    clear_tv(&argv[1]);
+	    if (r == FAIL || called_emsg != called_emsg_start)
+		break;
+	}
+    }
     else
     {
 	blob_T	*b = argvars[0].vval.v_blob;
diff --git a/src/proto/typval.pro b/src/proto/typval.pro
index 675ad12..a62f3da 100644
--- a/src/proto/typval.pro
+++ b/src/proto/typval.pro
@@ -34,6 +34,7 @@
 int check_for_opt_string_or_number_arg(typval_T *args, int idx);
 int check_for_string_or_blob_arg(typval_T *args, int idx);
 int check_for_string_or_list_arg(typval_T *args, int idx);
+int check_for_string_or_list_or_blob_arg(typval_T *args, int idx);
 int check_for_opt_string_or_list_arg(typval_T *args, int idx);
 int check_for_string_or_dict_arg(typval_T *args, int idx);
 int check_for_string_or_number_or_list_arg(typval_T *args, int idx);
diff --git a/src/testdir/test_listdict.vim b/src/testdir/test_listdict.vim
index 30f47ad..c767313 100644
--- a/src/testdir/test_listdict.vim
+++ b/src/testdir/test_listdict.vim
@@ -1,4 +1,5 @@
 " Tests for the List and Dict types
+scriptencoding utf-8
 
 source vim9.vim
 
@@ -936,7 +937,7 @@
   call assert_fails("call sort([1, 2], function('min'))", "E118:")
 endfunc
 
-" reduce a list or a blob
+" reduce a list, blob or string
 func Test_reduce()
   let lines =<< trim END
       call assert_equal(1, reduce([], LSTART acc, val LMIDDLE acc + val LEND, 1))
@@ -959,6 +960,16 @@
 
       call assert_equal(0xff, reduce(0zff, LSTART acc, val LMIDDLE acc + val LEND))
       call assert_equal(2 * (2 * 0xaf + 0xbf) + 0xcf, reduce(0zAFBFCF, LSTART acc, val LMIDDLE 2 * acc + val LEND))
+
+      call assert_equal('x,y,z', 'xyz'->reduce(LSTART acc, val LMIDDLE acc .. ',' .. val LEND))
+      call assert_equal('', ''->reduce(LSTART acc, val LMIDDLE acc .. ',' .. val LEND, ''))
+      call assert_equal('あ,い,う,え,お,😊,💕', 'あいうえお😊💕'->reduce(LSTART acc, val LMIDDLE acc .. ',' .. val LEND))
+      call assert_equal('😊,あ,い,う,え,お,💕', 'あいうえお💕'->reduce(LSTART acc, val LMIDDLE acc .. ',' .. val LEND, '😊'))
+      call assert_equal('ऊ,ॠ,ॡ', reduce('ऊॠॡ', LSTART acc, val LMIDDLE acc .. ',' .. val LEND))
+      call assert_equal('c,à,t', reduce('càt', LSTART acc, val LMIDDLE acc .. ',' .. val LEND))
+      call assert_equal('Å,s,t,r,ö,m', reduce('Åström', LSTART acc, val LMIDDLE acc .. ',' .. val LEND))
+      call assert_equal('Å,s,t,r,ö,m', reduce('Åström', LSTART acc, val LMIDDLE acc .. ',' .. val LEND))
+      call assert_equal(',a,b,c', reduce('abc', LSTART acc, val LMIDDLE acc .. ',' .. val LEND, test_null_string()))
   END
   call CheckLegacyAndVim9Success(lines)
 
@@ -967,13 +978,23 @@
 
   call assert_fails("call reduce([], { acc, val -> acc + val })", 'E998: Reduce of an empty List with no initial value')
   call assert_fails("call reduce(0z, { acc, val -> acc + val })", 'E998: Reduce of an empty Blob with no initial value')
+  call assert_fails("call reduce('', { acc, val -> acc + val })", 'E998: Reduce of an empty String with no initial value')
+  call assert_fails("call reduce(test_null_string(), { acc, val -> acc + val })", 'E998: Reduce of an empty String with no initial value')
 
-  call assert_fails("call reduce({}, { acc, val -> acc + val }, 1)", 'E897:')
-  call assert_fails("call reduce(0, { acc, val -> acc + val }, 1)", 'E897:')
-  call assert_fails("call reduce('', { acc, val -> acc + val }, 1)", 'E897:')
+  call assert_fails("call reduce({}, { acc, val -> acc + val }, 1)", 'E1098:')
+  call assert_fails("call reduce(0, { acc, val -> acc + val }, 1)", 'E1098:')
   call assert_fails("call reduce([1, 2], 'Xdoes_not_exist')", 'E117:')
   call assert_fails("echo reduce(0z01, { acc, val -> 2 * acc + val }, '')", 'E39:')
 
+  call assert_fails("vim9 reduce(0, (acc, val) => (acc .. val), '')", 'E1252:')
+  call assert_fails("vim9 reduce({}, (acc, val) => (acc .. val), '')", 'E1252:')
+  call assert_fails("vim9 reduce(0.1, (acc, val) => (acc .. val), '')", 'E1252:')
+  call assert_fails("vim9 reduce(function('tr'), (acc, val) => (acc .. val), '')", 'E1252:')
+  call assert_fails("call reduce('', { acc, val -> acc + val }, 1)", 'E1253:')
+  call assert_fails("call reduce('', { acc, val -> acc + val }, {})", 'E1253:')
+  call assert_fails("call reduce('', { acc, val -> acc + val }, 0.1)", 'E1253:')
+  call assert_fails("call reduce('', { acc, val -> acc + val }, function('tr'))", 'E1253:')
+
   let g:lut = [1, 2, 3, 4]
   func EvilRemove()
     call remove(g:lut, 1)
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index aa5af0d..a6d8984 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -1232,7 +1232,7 @@
 enddef
 
 def Test_filter()
-  CheckDefAndScriptFailure2(['filter(1.1, "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got float', 'E1228: List, Dictionary, Blob or String required for argument 1')
+  CheckDefAndScriptFailure2(['filter(1.1, "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got float', 'E1251: List, Dictionary, Blob or String required for argument 1')
   assert_equal([], filter([1, 2, 3], '0'))
   assert_equal([1, 2, 3], filter([1, 2, 3], '1'))
   assert_equal({b: 20}, filter({a: 10, b: 20}, 'v:val == 20'))
@@ -2028,9 +2028,9 @@
 
 def Test_map()
   if has('channel')
-    CheckDefAndScriptFailure2(['map(test_null_channel(), "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got channel', 'E1228: List, Dictionary, Blob or String required for argument 1')
+    CheckDefAndScriptFailure2(['map(test_null_channel(), "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got channel', 'E1251: List, Dictionary, Blob or String required for argument 1')
   endif
-  CheckDefAndScriptFailure2(['map(1, "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got number', 'E1228: List, Dictionary, Blob or String required for argument 1')
+  CheckDefAndScriptFailure2(['map(1, "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got number', 'E1251: List, Dictionary, Blob or String required for argument 1')
 enddef
 
 def Test_map_failure()
@@ -2147,9 +2147,9 @@
 
 def Test_mapnew()
   if has('channel')
-    CheckDefAndScriptFailure2(['mapnew(test_null_job(), "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got job', 'E1228: List, Dictionary, Blob or String required for argument 1')
+    CheckDefAndScriptFailure2(['mapnew(test_null_job(), "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got job', 'E1251: List, Dictionary, Blob or String required for argument 1')
   endif
-  CheckDefAndScriptFailure2(['mapnew(1, "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got number', 'E1228: List, Dictionary, Blob or String required for argument 1')
+  CheckDefAndScriptFailure2(['mapnew(1, "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got number', 'E1251: List, Dictionary, Blob or String required for argument 1')
 enddef
 
 def Test_mapset()
@@ -2682,7 +2682,7 @@
 enddef
 
 def Test_reduce()
-  CheckDefAndScriptFailure2(['reduce({a: 10}, "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got dict<number>', 'E897: List or Blob required')
+  CheckDefAndScriptFailure2(['reduce({a: 10}, "1")'], 'E1013: Argument 1: type mismatch, expected list<any> but got dict<number>', 'E1252: String, List or Blob required for argument 1')
   assert_equal(6, [1, 2, 3]->reduce((r, c) => r + c, 0))
   assert_equal(11, 0z0506->reduce((r, c) => r + c, 0))
 enddef
diff --git a/src/typval.c b/src/typval.c
index 09381f2..7716873 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -663,6 +663,23 @@
 }
 
 /*
+ * Give an error and return FAIL unless "args[idx]" is a string, a list or a
+ * blob.
+ */
+    int
+check_for_string_or_list_or_blob_arg(typval_T *args, int idx)
+{
+    if (args[idx].v_type != VAR_STRING
+	    && args[idx].v_type != VAR_LIST
+	    && args[idx].v_type != VAR_BLOB)
+    {
+	semsg(_(e_string_list_or_blob_required_for_argument_nr), idx + 1);
+	return FAIL;
+    }
+    return OK;
+}
+
+/*
  * Check for an optional string or list argument at 'idx'
  */
     int
@@ -697,10 +714,7 @@
 	    && args[idx].v_type != VAR_NUMBER
 	    && args[idx].v_type != VAR_LIST)
     {
-	if (idx >= 0)
-	    semsg(_(e_string_number_or_list_required_for_argument_nr), idx + 1);
-	else
-	    emsg(_(e_stringreq));
+	semsg(_(e_string_number_or_list_required_for_argument_nr), idx + 1);
 	return FAIL;
     }
     return OK;
@@ -742,10 +756,7 @@
 {
     if (args[idx].v_type != VAR_LIST && args[idx].v_type != VAR_BLOB)
     {
-	if (idx >= 0)
-	    semsg(_(e_list_or_blob_required_for_argument_nr), idx + 1);
-	else
-	    emsg(_(e_listreq));
+	semsg(_(e_list_or_blob_required_for_argument_nr), idx + 1);
 	return FAIL;
     }
     return OK;
diff --git a/src/version.c b/src/version.c
index 8ae0a86..d99e18c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -750,6 +750,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3848,
+/**/
     3847,
 /**/
     3846,