diff --git a/lib/stdlib/src/erl_lint.erl b/lib/stdlib/src/erl_lint.erl
index d8825d677af2..8732b1743b50 100644
--- a/lib/stdlib/src/erl_lint.erl
+++ b/lib/stdlib/src/erl_lint.erl
@@ -74,7 +74,7 @@ Module:format_error(ErrorDescriptor)
 -export([is_guard_expr/1]).
 -export([bool_option/4,value_option/3,value_option/7]).
 
--export([check_format_string/1]).
+-export([check_format_string/1, check_format_string/2]).
 
 -export_type([error_info/0, error_description/0]).
 -export_type([fun_used_vars/0]). % Used from erl_eval.erl.
@@ -4593,7 +4593,7 @@ check_format_2a(Fmt, FmtAnno, As) ->
     end.
 
 check_format_3(Fmt, FmtAnno, As) ->
-    case check_format_string(Fmt) of
+    case check_format_string(Fmt, true) of
         {ok,Need} ->
             check_format_4(Need, FmtAnno, As);
         {error,S} ->
@@ -4643,99 +4643,101 @@ args_list(_Other) -> 'maybe'.
 args_length({cons,_A,_H,T}) -> 1 + args_length(T);
 args_length({nil,_A}) -> 0.
 
+
 -doc false.
-check_format_string(Fmt) when is_atom(Fmt) ->
-    check_format_string(atom_to_list(Fmt));
-check_format_string(Fmt) when is_binary(Fmt) ->
-    check_format_string(binary_to_list(Fmt));
 check_format_string(Fmt) ->
-    extract_sequences(Fmt, []).
+    check_format_string(Fmt, true).
 
-extract_sequences(Fmt, Need0) ->
+-doc false.
+check_format_string(Fmt, Strict) when is_atom(Fmt) ->
+    check_format_string(atom_to_list(Fmt), Strict);
+check_format_string(Fmt, Strict) when is_binary(Fmt) ->
+    check_format_string(binary_to_list(Fmt), Strict);
+check_format_string(Fmt, Strict) ->
+    extract_sequences(Fmt, [], Strict).
+
+extract_sequences(Fmt, Need0, Strict) ->
     case string:find(Fmt, [$~]) of
         nomatch -> {ok,lists:reverse(Need0)};         %That's it
         [$~|Fmt1] ->
-            case extract_sequence(1, Fmt1, Need0) of
-                {ok,Need1,Rest} -> extract_sequences(Rest, Need1);
+            case extract_sequence(1, Fmt1, Need0, Strict) of
+                {ok,Need1,Rest} -> extract_sequences(Rest, Need1, Strict);
                 Error -> Error
             end
     end.
 
-extract_sequence(1, [$-,C|Fmt], Need)
+extract_sequence(1, [$-,C|Fmt], Need, Strict)
   when is_integer(C), C >= $0, C =< $9 ->
-    extract_sequence_digits(1, Fmt, Need);
-extract_sequence(1, [C|Fmt], Need)
+    extract_sequence_digits(1, Fmt, Need, Strict);
+extract_sequence(1, [C|Fmt], Need, Strict)
   when is_integer(C), C >= $0, C =< $9 ->
-    extract_sequence_digits(1, Fmt, Need);
-extract_sequence(1, [$-,$*|Fmt], Need) ->
-    extract_sequence(2, Fmt, [int|Need]);
-extract_sequence(1, [$*|Fmt], Need) ->
-    extract_sequence(2, Fmt, [int|Need]);
-extract_sequence(1, Fmt, Need) ->
-    extract_sequence(2, Fmt, Need);
-
-extract_sequence(2, [$.,C|Fmt], Need)
+    extract_sequence_digits(1, Fmt, Need, Strict);
+extract_sequence(1, [$-,$*|Fmt], Need, Strict) ->
+    extract_sequence(2, Fmt, [int|Need], Strict);
+extract_sequence(1, [$*|Fmt], Need, Strict) ->
+    extract_sequence(2, Fmt, [int|Need], Strict);
+extract_sequence(1, Fmt, Need, Strict) ->
+    extract_sequence(2, Fmt, Need, Strict);
+
+extract_sequence(2, [$.,C|Fmt], Need, Strict)
   when is_integer(C), C >= $0, C =< $9 ->
-    extract_sequence_digits(2, Fmt, Need);
-extract_sequence(2, [$.,$*|Fmt], Need) ->
-    extract_sequence(3, Fmt, [int|Need]);
-extract_sequence(2, [$.|Fmt], Need) ->
-    extract_sequence(3, Fmt, Need);
-extract_sequence(2, Fmt, Need) ->
-    extract_sequence(4, Fmt, Need);
-
-extract_sequence(3, [$.,$*|Fmt], Need) ->
-    extract_sequence(4, Fmt, [int|Need]);
-extract_sequence(3, [$.,_|Fmt], Need) ->
-    extract_sequence(4, Fmt, Need);
-extract_sequence(3, Fmt, Need) ->
-    extract_sequence(4, Fmt, Need);
-
-extract_sequence(4, Fmt0, Need) ->
-    case extract_modifiers(Fmt0, []) of
+    extract_sequence_digits(2, Fmt, Need, Strict);
+extract_sequence(2, [$.,$*|Fmt], Need, Strict) ->
+    extract_sequence(3, Fmt, [int|Need], Strict);
+extract_sequence(2, [$.|Fmt], Need, Strict) ->
+    extract_sequence(3, Fmt, Need, Strict);
+extract_sequence(2, Fmt, Need, Strict) ->
+    extract_sequence(4, Fmt, Need, Strict);
+
+extract_sequence(3, [$.,$*|Fmt], Need, Strict) ->
+    extract_sequence(4, Fmt, [int|Need], Strict);
+extract_sequence(3, [$.,_|Fmt], Need, Strict) ->
+    extract_sequence(4, Fmt, Need, Strict);
+extract_sequence(3, Fmt, Need, Strict) ->
+    extract_sequence(4, Fmt, Need, Strict);
+
+extract_sequence(4, Fmt0, Need0, Strict) ->
+    case extract_modifiers(Fmt0, [], Need0, Strict) of
         {error, _} = Error ->
             Error;
-        {[C|Fmt], Modifiers} ->
+        {[C|Fmt], Modifiers, Need1} when Strict ->
             maybe
                 ok ?= check_modifiers(C, Modifiers),
-                case ordsets:is_element($K, Modifiers) of
-                    true ->
-                        extract_sequence(5, [C|Fmt], ['fun'|Need]);
-                    false ->
-                        extract_sequence(5, [C|Fmt], Need)
-                end
+                extract_sequence(5, [C|Fmt], Need1, Strict)
             end;
-        {[], _} ->
-            extract_sequence(5, [], Need)
+        {Fmt, _, Need1} ->
+            extract_sequence(5, Fmt, Need1, Strict)
     end;
 
-extract_sequence(5, [C|Fmt], Need0) ->
+extract_sequence(5, [C|Fmt], Need0, _Strict) ->
     case control_type(C, Need0) of
         error -> {error,"invalid control ~" ++ [C]};
         Need1 -> {ok,Need1,Fmt}
     end;
-extract_sequence(_, [], _Need) -> {error,"truncated"}.
+extract_sequence(_, [], _Need, _Strict) -> {error,"truncated"}.
 
-extract_sequence_digits(Fld, [C|Fmt], Need)
+extract_sequence_digits(Fld, [C|Fmt], Need, Strict)
   when is_integer(C), C >= $0, C =< $9 ->
-    extract_sequence_digits(Fld, Fmt, Need);
-extract_sequence_digits(Fld, Fmt, Need) ->
-    extract_sequence(Fld+1, Fmt, Need).
+    extract_sequence_digits(Fld, Fmt, Need, Strict);
+extract_sequence_digits(Fld, Fmt, Need, Strict) ->
+    extract_sequence(Fld+1, Fmt, Need, Strict).
 
-extract_modifiers([C|Fmt], Modifiers0) ->
-    case is_modifier(C) of
-        true ->
+extract_modifiers([C|Fmt], Modifiers0, Need0, Strict) ->
+    case is_modifier(C, Need0) of
+	{true, Need1} when Strict ->
             case ordsets:add_element(C, Modifiers0) of
                 Modifiers0 ->
                     {error, "repeated modifier " ++ [C]};
                 Modifiers ->
-                    extract_modifiers(Fmt, Modifiers)
+                    extract_modifiers(Fmt, Modifiers, Need1, Strict)
             end;
+	{true, Need1} ->
+	    extract_modifiers(Fmt, ordsets:add_element(C, Modifiers0), Need1, Strict);
         false ->
-            {[C|Fmt], Modifiers0}
+            {[C|Fmt], Modifiers0, Need0}
     end;
-extract_modifiers([], Modifiers) ->
-    {[], Modifiers}.
+extract_modifiers([], Modifiers, Need, _Strict) ->
+    {[], Modifiers, Need}.
 
 check_modifiers(C, Modifiers) ->
     maybe
@@ -4760,11 +4762,11 @@ check_modifiers_1(M, Modifiers, C, Cs) ->
             {error, "conflicting modifiers ~" ++ M ++ [C]}
     end.
 
-is_modifier($k) -> true;
-is_modifier($K) -> true;
-is_modifier($l) -> true;
-is_modifier($t) -> true;
-is_modifier(_) -> false.
+is_modifier($k, Need) -> {true, Need};
+is_modifier($K, Need) -> {true, ['fun'|Need]};
+is_modifier($l, Need) -> {true, Need};
+is_modifier($t, Need) -> {true, Need};
+is_modifier(_, _) -> false.
 
 control_type($~, Need) -> Need;
 control_type($c, Need) -> [int|Need];
diff --git a/lib/stdlib/src/erl_stdlib_errors.erl b/lib/stdlib/src/erl_stdlib_errors.erl
index 8403e144c462..8105be712b8c 100644
--- a/lib/stdlib/src/erl_stdlib_errors.erl
+++ b/lib/stdlib/src/erl_stdlib_errors.erl
@@ -540,7 +540,7 @@ check_io_format([Fmt, Args], Cause) ->
         _ when not is_list(Args) ->
                 [[],must_be_list(Args)];
         true ->
-            case erl_lint:check_format_string(Fmt) of
+            case erl_lint:check_format_string(Fmt, false) of
                 {error,S} ->
                     [io_lib:format("format string invalid (~ts)",[S])];
                 {ok,ArgTypes} when length(ArgTypes) =/= length(Args) ->
@@ -587,6 +587,11 @@ check_io_arguments([], [], _No) ->
     [];
 check_io_arguments([Type|TypeT], [Arg|ArgT], No) ->
     case Type of
+	'fun' when Arg =:= undefined; Arg =:= ordered; Arg =:= reversed; is_function(Arg, 2) ->
+	    check_io_arguments(TypeT, ArgT, No+1);
+	'fun' ->
+	    [io_lib:format("element ~B must be 'undefined', 'ordered', 'reversed', or a fun that takes two arguments", [No]) |
+	     check_io_arguments(TypeT, ArgT, No+1)];
         float when is_float(Arg) ->
             check_io_arguments(TypeT, ArgT, No+1);
         int when is_integer(Arg) ->
@@ -1157,7 +1162,7 @@ expand_error(not_integer) ->
 expand_error(not_list) ->
     <<"not a list">>;
 expand_error(not_map_iterator_order) ->
-    <<"not 'undefined', 'ordered', or a fun that takes two arguments">>;
+    <<"not 'undefined', 'ordered', 'reversed', or a fun that takes two arguments">>;
 expand_error(not_map_or_iterator) ->
     <<"not a map or an iterator">>;
 expand_error(not_number) ->
diff --git a/lib/stdlib/test/erl_lint_SUITE.erl b/lib/stdlib/test/erl_lint_SUITE.erl
index ffeb7c2e1190..1bb6c8c3b398 100644
--- a/lib/stdlib/test/erl_lint_SUITE.erl
+++ b/lib/stdlib/test/erl_lint_SUITE.erl
@@ -3819,7 +3819,7 @@ otp_8051(Config) when is_list(Config) ->
 
 %% Check that format warnings are generated.
 format_warn(Config) when is_list(Config) ->
-    L1 = 16,
+    L1 = 23,
     L2 = 5,
     format_level(1, L1, Config),
     format_level(2, L1+L2, Config),
diff --git a/lib/stdlib/test/erl_lint_SUITE_data/format.erl b/lib/stdlib/test/erl_lint_SUITE_data/format.erl
index 8b14c7144775..1c4c81e6c41e 100644
--- a/lib/stdlib/test/erl_lint_SUITE_data/format.erl
+++ b/lib/stdlib/test/erl_lint_SUITE_data/format.erl
@@ -51,6 +51,14 @@ f(F) ->
     io:format("~14p", [F]),
     io:format("~*p", [a, F]),			%no type checking
     io:format("~*p", [14, F]),
+    
+    io:format("~tlp", [F]),			%1
+    io:format("~kKp", [undefined, F]),		%1
+    io:format("~tb", [1]),			%1
+    io:format("~lb", [1]),			%1
+    io:format("~kb", [1]),			%1
+    io:format("~Kb", [undefined, 1]),		%1
+    io:format("~llp", [F]),			%1
 
     io:fwrite("~p", []),			%1
     io_lib:format("~p", []),			%1
diff --git a/lib/stdlib/test/io_SUITE.erl b/lib/stdlib/test/io_SUITE.erl
index 877e4eec75f7..82fc97f6b4c8 100644
--- a/lib/stdlib/test/io_SUITE.erl
+++ b/lib/stdlib/test/io_SUITE.erl
@@ -3135,7 +3135,15 @@ error_info(Config) ->
            {Format,["~s",["Спутник-1"]],[{1,"failed to format string"}]},
            {Format,["~s",[1]],[{2,"1 must be of type string"}]},
            {Format,["~s~s",[a,1]],[{2,"2 must be of type string"}]},
-           {Format,["~s",[[a]]],[{2,"1 must be of type string"}]}] || Format <- [format,fwrite]]
+           {Format,["~s",[[a]]],[{2,"1 must be of type string"}]},
+
+	   %% Ensure error messages contain the correct reason (GH-8568)
+	   {Format, ["~ltkKltkKp", []], [{1,"wrong number of arguments"}]},
+	   {Format, ["~ltkKltkKm", [undefined, ordered, a]], [{1,"format string"}]},
+	   {Format, ["~ltkKltkKb", [undefined, ordered, a]], [{2,"3 must be of type integer"}]},
+	   {Format, ["~ltkKp", [foo, #{a => b}]], [{2,"1 must be 'undefined', 'ordered', 'reversed', or a fun that takes two arguments"}]}
+	  ]
+	  || Format <- [format,fwrite]]
 
         ],