diff --git a/src/evalfunc.c b/src/evalfunc.c
index 9e0fd80..03d6459 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -486,6 +486,52 @@
 }
 
 /*
+ * Check second argument of filter(): func must return a bool.
+ */
+    static int
+arg_filter_func(type_T *type, argcontext_T *context)
+{
+    if (type->tt_type == VAR_FUNC
+	    && !(type->tt_member->tt_type == VAR_BOOL
+		|| type->tt_member->tt_type == VAR_NUMBER
+		|| type->tt_member->tt_type == VAR_ANY))
+    {
+	arg_type_mismatch(&t_func_bool, type, context->arg_idx + 1);
+	return FAIL;
+    }
+    return OK;
+}
+
+/*
+ * Check second argument of map().
+ */
+    static int
+arg_map_func(type_T *type, argcontext_T *context)
+{
+    if (type->tt_type == VAR_FUNC
+	    && type->tt_member != &t_any
+	    && type->tt_member != &t_unknown)
+    {
+	type_T *expected = NULL;
+
+	if (context->arg_types[0]->tt_type == VAR_LIST
+		|| context->arg_types[0]->tt_type == VAR_DICT)
+	    expected = context->arg_types[0]->tt_member;
+	else if (context->arg_types[0]->tt_type == VAR_STRING
+		|| context->arg_types[0]->tt_type == VAR_BLOB)
+	    expected = &t_number;
+	if (expected != NULL)
+	{
+	    type_T t_func_exp = {VAR_FUNC, -1, 0, TTFLAG_STATIC,
+							       expected, NULL};
+
+	    return check_arg_type(&t_func_exp, type, context);
+	}
+    }
+    return OK;
+}
+
+/*
  * Check "type" is a list of 'any' or a blob or a string.
  */
     static int
@@ -859,7 +905,9 @@
 static argcheck_T arg1_len[] = {arg_len1};
 static argcheck_T arg3_libcall[] = {arg_string, arg_string, arg_string_or_nr};
 static argcheck_T arg14_maparg[] = {arg_string, arg_string, arg_bool, arg_bool};
-static argcheck_T arg2_mapfilter[] = {arg_list_or_dict_or_blob_or_string, NULL};
+static argcheck_T arg2_filter[] = {arg_list_or_dict_or_blob_or_string, arg_filter_func};
+static argcheck_T arg2_map[] = {arg_list_or_dict_or_blob_or_string, arg_map_func};
+static argcheck_T arg2_mapnew[] = {arg_list_or_dict_or_blob_or_string, NULL};
 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};
@@ -1437,7 +1485,7 @@
 			ret_number_bool,    f_filereadable},
     {"filewritable",	1, 1, FEARG_1,	    arg1_string,
 			ret_number,	    f_filewritable},
-    {"filter",		2, 2, FEARG_1,	    arg2_mapfilter,
+    {"filter",		2, 2, FEARG_1,	    arg2_filter,
 			ret_first_arg,	    f_filter},
     {"finddir",		1, 3, FEARG_1,	    arg3_string_string_number,
 			ret_finddir,	    f_finddir},
@@ -1703,13 +1751,13 @@
 		NULL
 #endif
 			},
-    {"map",		2, 2, FEARG_1,	    arg2_mapfilter,
+    {"map",		2, 2, FEARG_1,	    arg2_map,
 			ret_first_cont,	    f_map},
     {"maparg",		1, 4, FEARG_1,	    arg14_maparg,
 			ret_maparg,	    f_maparg},
     {"mapcheck",	1, 3, FEARG_1,	    arg3_string_string_bool,
 			ret_string,	    f_mapcheck},
-    {"mapnew",		2, 2, FEARG_1,	    arg2_mapfilter,
+    {"mapnew",		2, 2, FEARG_1,	    arg2_mapnew,
 			ret_first_cont,	    f_mapnew},
     {"mapset",		3, 3, FEARG_1,	    arg3_string_bool_dict,
 			ret_void,	    f_mapset},
diff --git a/src/globals.h b/src/globals.h
index 45561de..038d680 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -432,6 +432,7 @@
 EXTERN type_T t_func_any INIT6(VAR_FUNC, -1, 0, TTFLAG_STATIC, &t_any, NULL);
 EXTERN type_T t_func_number INIT6(VAR_FUNC, -1, 0, TTFLAG_STATIC, &t_number, NULL);
 EXTERN type_T t_func_string INIT6(VAR_FUNC, -1, 0, TTFLAG_STATIC, &t_string, NULL);
+EXTERN type_T t_func_bool INIT6(VAR_FUNC, -1, 0, TTFLAG_STATIC, &t_bool, NULL);
 EXTERN type_T t_func_0_void INIT6(VAR_FUNC, 0, 0, TTFLAG_STATIC, &t_void, NULL);
 EXTERN type_T t_func_0_any INIT6(VAR_FUNC, 0, 0, TTFLAG_STATIC, &t_any, NULL);
 EXTERN type_T t_func_0_number INIT6(VAR_FUNC, 0, 0, TTFLAG_STATIC, &t_number, NULL);
diff --git a/src/list.c b/src/list.c
index 61a26a3..6fafef6 100644
--- a/src/list.c
+++ b/src/list.c
@@ -2280,7 +2280,7 @@
 
 	// filter(): when expr is zero remove the item
 	if (in_vim9script())
-	    *remp = !tv2bool(newtv);
+	    *remp = !tv_get_bool_chk(newtv, &error);
 	else
 	    *remp = (tv_get_number_chk(newtv, &error) == 0);
 	clear_tv(newtv);
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index 547a213..43b9d33 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -1241,6 +1241,15 @@
 
 def Test_filter()
   CheckDefAndScriptFailure(['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'])
+
+  var lines =<< trim END
+    def F(i: number, v: any): string
+      return 'bad'
+    enddef
+    echo filter([1, 2, 3], F)
+  END
+  CheckDefAndScriptFailure(lines, ['E1013: Argument 2: type mismatch, expected func(...): bool', 'E1135: Using a String as a Bool:'])
+
   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'))
@@ -2141,6 +2150,14 @@
       range(3)->map((a, b, c, d) => a + b + c + d)
   END
   CheckDefExecAndScriptFailure(lines, 'E1190: 2 arguments too few')
+
+  lines =<< trim END
+    def Map(i: number, v: number): string
+      return 'bad'
+    enddef
+    echo map([1, 2, 3], Map)
+  END
+  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()'])
 enddef
 
 def Test_map_item_type()
@@ -2155,19 +2172,19 @@
     var l: list<number> = [0]
     echo map(l, (_, v) => [])
   END
-  CheckDefExecAndScriptFailure(lines, 'E1012: Type mismatch; expected number but got list<unknown> in map()', 2)
+  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)
 
   lines =<< trim END
     var l: list<number> = range(2)
     echo map(l, (_, v) => [])
   END
-  CheckDefExecAndScriptFailure(lines, 'E1012: Type mismatch; expected number but got list<unknown> in map()', 2)
+  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)
 
   lines =<< trim END
     var d: dict<number> = {key: 0}
     echo map(d, (_, v) => [])
   END
-  CheckDefExecAndScriptFailure(lines, 'E1012: Type mismatch; expected number but got list<unknown> in map()', 2)
+  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)
 enddef
 
 def Test_maparg()
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index 9cf035a..01b4538 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -2077,7 +2077,7 @@
             )
       assert_equal([111, 222, 111], ll)
 
-      var dl = [{key: 0}, {key: 22}]->filter(( _, v) => v['key'] )
+      var dl = [{key: 0}, {key: 22}]->filter(( _, v) => !!v['key'] )
       assert_equal([{key: 22}], dl)
 
       dl = [{key: 12}, {['foo']: 34}]
@@ -2236,7 +2236,7 @@
             )
       assert_equal([111, 222, 111], ll)
 
-      var dl = [{key: 0}, {key: 22}]->filter(( _, v) => v['key'] )
+      var dl = [{key: 0}, {key: 22}]->filter(( _, v) => !!v['key'] )
       assert_equal([{key: 22}], dl)
 
       dl = [{key: 12}, {['foo']: 34}]
@@ -2308,7 +2308,7 @@
   lines =<< trim END
       search('"', 'cW', 0, 0, () =>
 	synstack('.', col('.'))
-          ->map((_, v) => synIDattr(v, 'name'))->len())
+          ->mapnew((_, v) => synIDattr(v, 'name'))->len())
   END
   CheckDefAndScriptSuccess(lines)
 enddef
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index dcfe888..8975e1b 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -2048,7 +2048,7 @@
       return idx % 2 == 1
     enddef
     export def FastFilter(): list<number>
-      return range(10)->filter('FilterFunc')
+      return range(10)->filter('FilterFunc(v:key, v:val)')
     enddef
     export def FastFilterDirect(): list<number>
       return range(10)->filter(FilterFunc)
diff --git a/src/version.c b/src/version.c
index a09a0bf..adb3722 100644
--- a/src/version.c
+++ b/src/version.c
@@ -750,6 +750,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3897,
+/**/
     3896,
 /**/
     3895,