diff --git a/src/jsx_encoder.erl b/src/jsx_encoder.erl
index 9c10a19..21e5269 100644
--- a/src/jsx_encoder.erl
+++ b/src/jsx_encoder.erl
@@ -165,6 +165,8 @@ clean_string(<<237, X, _, Rest/binary>>, Acc) when X >= 160 ->
     clean_string(Rest, <<Acc/binary, 16#fffd/utf8>>);
 clean_string(<<239, 183, X, Rest/binary>>, Acc) when X >= 144, X =< 175 ->
     clean_string(Rest, <<Acc/binary, 16#fffd/utf8>>);
+clean_string(<<239, 191, X, Rest/binary>>, Acc) when X == 190, X == 191 ->
+    clean_string(Rest, <<Acc/binary, 16#fffd/utf8>>);
 clean_string(<<C/utf8, Rest/binary>>, Acc) ->
     clean_string(Rest, <<Acc/binary, C/utf8>>);
 clean_string(<<_, Rest/binary>>, Acc) ->