diff --git a/src/evalfunc.c b/src/evalfunc.c
index 7c313f5..86e5d2f 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -517,7 +517,7 @@
 }
 
 /*
- * Check second argument of map().
+ * Check second argument of map(), the function.
  */
     static int
 arg_map_func(type_T *type, type_T *decl_type UNUSED, argcontext_T *context)
@@ -530,34 +530,66 @@
 
     if (type->tt_type == VAR_FUNC)
     {
-	if (type->tt_member != &t_any && type->tt_member != &t_unknown)
+	type_T *expected_ret = NULL;
+	type_T *(args[2]);
+	type_T t_func_exp = {VAR_FUNC, 2, 0, 0, NULL, args};
+
+	if (context->arg_types[0].type_curr->tt_type == VAR_LIST
+		|| context->arg_types[0].type_curr->tt_type == VAR_DICT)
 	{
-	    type_T *expected = NULL;
+	    // Use the declared type if possible, so that an error is given if
+	    // a declared list changes type, but not if a constant list changes
+	    // type.
+	    if (context->arg_types[0].type_decl->tt_type == VAR_LIST
+		    || context->arg_types[0].type_decl->tt_type == VAR_DICT)
+		expected_ret = context->arg_types[0].type_decl->tt_member;
+	    else
+		expected_ret = context->arg_types[0].type_curr->tt_member;
+	}
+	else if (context->arg_types[0].type_curr->tt_type == VAR_STRING)
+	    expected_ret = &t_string;
+	else if (context->arg_types[0].type_curr->tt_type == VAR_BLOB)
+	    expected_ret = &t_number;
 
-	    if (context->arg_types[0].type_curr->tt_type == VAR_LIST
-		    || context->arg_types[0].type_curr->tt_type == VAR_DICT)
+	args[0] = NULL;
+	args[1] = &t_unknown;
+	if (type->tt_argcount != -1)
+	{
+	    if (!(type->tt_argcount == 2 || (type->tt_argcount == 1
+					&& (type->tt_flags & TTFLAG_VARARGS))))
 	    {
-		// Use the declared type, so that an error is given if a
-		// declared list changes type, but not if a constant list
-		// changes type.
-		if (context->arg_types[0].type_decl->tt_type == VAR_LIST
-			|| context->arg_types[0].type_decl->tt_type == VAR_DICT)
-		    expected = context->arg_types[0].type_decl->tt_member;
-		else
-		    expected = context->arg_types[0].type_curr->tt_member;
+		emsg(_(e_invalid_number_of_arguments));
+		return FAIL;
 	    }
-	    else if (context->arg_types[0].type_curr->tt_type == VAR_STRING)
-		expected = &t_string;
-	    else if (context->arg_types[0].type_curr->tt_type == VAR_BLOB)
-		expected = &t_number;
-	    if (expected != NULL)
+	    if (type->tt_flags & TTFLAG_VARARGS)
+		// check the argument types at runtime
+		t_func_exp.tt_argcount = -1;
+	    else
 	    {
-		type_T t_func_exp = {VAR_FUNC, -1, 0, TTFLAG_STATIC,
-								   NULL, NULL};
+		if (context->arg_types[0].type_decl->tt_type == VAR_LIST)
+		    args[0] = &t_number;
+		else if (context->arg_types[0].type_decl->tt_type == VAR_DICT)
+		    args[0] = &t_string;
+		if (args[0] != NULL)
+		    args[1] = expected_ret;
+	    }
+	}
 
-		t_func_exp.tt_member = expected;
-		return check_arg_type(&t_func_exp, type, context);
-	    }
+	if ((type->tt_member != &t_any && type->tt_member != &t_unknown)
+		|| args[0] != NULL)
+	{
+	    where_T where = WHERE_INIT;
+
+	    t_func_exp.tt_member = expected_ret == NULL
+					|| type->tt_member == &t_any
+					|| type->tt_member == &t_unknown
+				    ? &t_any : expected_ret;
+	    if (args[0] == NULL)
+		args[0] = &t_unknown;
+	    return check_arg_type(&t_func_exp, type, context);
+
+	    where.wt_index = 2;
+	    return check_type(&t_func_exp, type, TRUE, where);
 	}
     }
     else
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index 09cfd70..882c181 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -2289,11 +2289,11 @@
   lines =<< trim END
       range(3)->map((a, b, c) => a + b + c)
   END
-  v9.CheckDefExecAndScriptFailure(lines, 'E1190: One argument too few')
+  v9.CheckDefAndScriptFailure(lines, ['E176:', 'E1190: One argument too few'])
   lines =<< trim END
       range(3)->map((a, b, c, d) => a + b + c + d)
   END
-  v9.CheckDefExecAndScriptFailure(lines, 'E1190: 2 arguments too few')
+  v9.CheckDefAndScriptFailure(lines, ['E176:', 'E1190: 2 arguments too few'])
 
   # declared list cannot change type
   lines =<< trim END
@@ -2303,7 +2303,7 @@
     var ll: list<number> = [1, 2, 3]
     echo map(ll, Map)
   END
-  v9.CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(...): number but got func(number, number): string', 'E1012: Type mismatch; expected number but got string in map()'])
+  v9.CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(?number, ?number): number but got func(number, number): string', 'E1012: Type mismatch; expected number but got string in map()'])
 
   # not declared list can change type
   echo [1, 2, 3]->map((..._) => 'x')
@@ -2321,19 +2321,19 @@
     var l: list<number> = [0]
     echo map(l, (_, v) => [])
   END
-  v9.CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(...): number but got func(any, any): list<unknown>', 'E1012: Type mismatch; expected number but got list<unknown> in map()'], 2)
+  v9.CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(?number, ?number): number but got func(any, any): list<unknown>', 'E1012: Type mismatch; expected number but got list<unknown> in map()'], 2)
 
   lines =<< trim END
     var l: list<number> = range(2)
     echo map(l, (_, v) => [])
   END
-  v9.CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(...): number but got func(any, any): list<unknown>', 'E1012: Type mismatch; expected number but got list<unknown> in map()'], 2)
+  v9.CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(?number, ?number): number but got func(any, any): list<unknown>', 'E1012: Type mismatch; expected number but got list<unknown> in map()'], 2)
 
   lines =<< trim END
     var d: dict<number> = {key: 0}
     echo map(d, (_, v) => [])
   END
-  v9.CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(...): number but got func(any, any): list<unknown>', 'E1012: Type mismatch; expected number but got list<unknown> in map()'], 2)
+  v9.CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(?string, ?number): number but got func(any, any): list<unknown>', 'E1012: Type mismatch; expected number but got list<unknown> in map()'], 2)
 enddef
 
 def Test_maparg()
@@ -2359,6 +2359,22 @@
   v9.CheckDefAndScriptFailure(['maparg("a", "b", 2)'], ['E1013: Argument 3: type mismatch, expected bool but got number', 'E1212: Bool required for argument 3'])
   v9.CheckDefAndScriptFailure(['maparg("a", "b", true, 2)'], ['E1013: Argument 4: type mismatch, expected bool but got number', 'E1212: Bool required for argument 4'])
   maparg('')->assert_equal('')
+
+  var lines =<< trim END
+      var l = [123]
+      l->map((_, v: string) => 0)
+  END
+  v9.CheckDefFailure(lines, 'E1013: Argument 2: type mismatch, expected func(?number, ?number): number but got func(any, string): number')
+
+  lines =<< trim END
+      ['x']->map((i: string, v: string) => 'y')
+  END
+  v9.CheckDefFailure(lines, 'E1013: Argument 2: type mismatch, expected func(?number, ?any): any but got func(string, string): string')
+
+  lines =<< trim END
+    {a: 1}->map((i: number, v: number) => 0)
+  END
+  v9.CheckDefFailure(lines, 'E1013: Argument 2: type mismatch, expected func(?string, ?any): any but got func(number, number): number')
 enddef
 
 def Test_maparg_mapset()
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index a7b6187..81a67d9 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -3732,12 +3732,12 @@
   var lines =<< trim END
     echo [0, 1, 2]->map(() => 123)
   END
-  v9.CheckDefExecAndScriptFailure(lines, 'E1106: 2 arguments too many', 1)
+  v9.CheckDefAndScriptFailure(lines, ['E176:', 'E1106: 2 arguments too many'], 1)
 
   lines =<< trim END
     echo [0, 1, 2]->map((_) => 123)
   END
-  v9.CheckDefExecAndScriptFailure(lines, 'E1106: One argument too many', 1)
+  v9.CheckDefAndScriptFailure(lines, ['E176', 'E1106: One argument too many'], 1)
 enddef
 
 def Test_closing_brace_at_start_of_line()
diff --git a/src/version.c b/src/version.c
index f151531..1fdf4e4 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4425,
+/**/
     4424,
 /**/
     4423,