diff --git a/src/str.erl b/src/str.erl
index 6aaa0c3..0847e0f 100644
--- a/src/str.erl
+++ b/src/str.erl
@@ -6,8 +6,8 @@
 %%% ```
 %%% str(Fmt, Args)     -> lists:flatten(io_lib:format(Fmt, Args))
 %%% bin(Fmt, Args)     -> list_to_binary(lists:flatten(io_lib:format(Fmt, Args)))
-%%% throw(Fmt, Args)   -> erlang:throw(lists:flatten(io_lib:format(Fmt, Args))
-%%% error(Fmt, Args)   -> erlang:error(lists:flatten(io_lib:format(Fmt, Args))
+%%% throw(Fmt, Args)   -> erlang:throw(list_to_binary(lists:flatten(io_lib:format(Fmt, Args)))
+%%% error(Fmt, Args)   -> erlang:error(list_to_binary(lists:flatten(io_lib:format(Fmt, Args)))
 %%% i2l(Int)           -> integer_to_list(Int)      % Enabled with compiled with
 %%%                                                 % the `{d,str_i2l}' option
 %%% b2l(Bin)           -> binary_to_list(Bin)       % Enabled with compiled with
@@ -168,12 +168,14 @@ update4(Arg, Node, Line, _Opt) when Arg==str; Arg==bin ->
       Node
   end;
 update4(I, Node, Line, _Opt) when I==throw; I==error ->
-  %% Replace throw(A, B) -> throw(lists:flatten(io_lib:format(A, B))).
-  %% Replace error(A, B) -> error(lists:flatten(io_lib:format(A, B))).
+  %% Replace throw(A, B) -> throw(list_to_binary(lists:flatten(io_lib:format(A, B)))).
+  %% Replace error(A, B) -> error(list_to_binary(lists:flatten(io_lib:format(A, B)))).
   put(line, Line),
   case erl_syntax:application_arguments(Node) of
     [A,B] ->
-      syn_call(I, [syn_call(lists, flatten, [syn_call(io_lib, format, [A,B])])]);
+      syn_call(I, [syn_call(erlang, list_to_binary,
+                            [syn_call(lists, flatten, [
+                                      syn_call(io_lib, format, [A,B])])])]);
     _ ->
       Node
   end;
diff --git a/test/str_test.erl b/test/str_test.erl
index 49746c8..925c573 100644
--- a/test/str_test.erl
+++ b/test/str_test.erl
@@ -39,11 +39,11 @@ str_test() ->
   ?assertEqual(<<"{a,1}">>,     bin({a, 1})).
 
 throw_test() ->
-  ?assertEqual("Test: 1", try throw("Test: ~w", [1]) catch throw:E -> E end),
-  ?assertEqual(ok,        try throw(ok)              catch throw:E -> E end).
+  ?assertEqual(<<"Test: 1">>, try throw("Test: ~w", [1]) catch throw:E -> E end),
+  ?assertEqual(ok,            try throw(ok)              catch throw:E -> E end).
 
 error_test() ->
-  ?assertEqual("Test: 1", try error("Test: ~w", [1]) catch error:E -> E end),
-  ?assertEqual(ok,        try error(ok)              catch error:E -> E end).
+  ?assertEqual(<<"Test: 1">>, try error("Test: ~w", [1]) catch error:E -> E end),
+  ?assertEqual(ok,            try error(ok)              catch error:E -> E end).
 
 -endif.