diff --git a/src/jsx_encoder.erl b/src/jsx_encoder.erl
index ee607c4..60bd4a0 100644
--- a/src/jsx_encoder.erl
+++ b/src/jsx_encoder.erl
@@ -286,7 +286,7 @@ pre_encoders_test_() ->
 error_test_() ->
     [
         {"value error", ?_assertError(badarg, encode(self(), []))},
-        {"string error", ?_assertError(badarg, encode(<<16#ffff/utf8>>, []))}
+        {"string error", ?_assertError(badarg, encode(<<239, 191, 191>>, []))}
     ].
 
 custom_error_handler_test_() ->
@@ -297,8 +297,8 @@ custom_error_handler_test_() ->
             encode(self(), [{error_handler, Error}])
         )},
         {"string error", ?_assertEqual(
-            {string, <<16#ffff/utf8>>},
-            encode(<<16#ffff/utf8>>, [{error_handler, Error}])
+            {string, <<239, 191, 191>>},
+            encode(<<239, 191, 191>>, [{error_handler, Error}])
         )}
     ].
 
diff --git a/src/jsx_parser.erl b/src/jsx_parser.erl
index a094ec3..ba572c8 100644
--- a/src/jsx_parser.erl
+++ b/src/jsx_parser.erl
@@ -214,7 +214,7 @@ error_test_() ->
         {"value error", ?_assertError(badarg, parse([self()], []))},
         {"maybe_done error", ?_assertError(badarg, parse([start_array, end_array, start_array, end_json], []))},
         {"done error", ?_assertError(badarg, parse([{string, <<"">>}, {literal, true}, end_json], []))},
-        {"string error", ?_assertError(badarg, parse([{string, <<16#ffff/utf8>>}, end_json], []))}
+        {"string error", ?_assertError(badarg, parse([{string, <<239, 191, 191>>}, end_json], []))}
     ].
 
 
@@ -234,8 +234,8 @@ custom_error_handler_test_() ->
             parse([{string, <<"">>}, {literal, true}, end_json], [{error_handler, Error}])
         )},
         {"string error", ?_assertEqual(
-            {string, [{string, <<16#ffff/utf8>>}, end_json]},
-            parse([{string, <<16#ffff/utf8>>}, end_json], [{error_handler, Error}])
+            {string, [{string, <<239, 191, 191>>}, end_json]},
+            parse([{string, <<239, 191, 191>>}, end_json], [{error_handler, Error}])
         )}
     ].