diff --git a/toml/lexer.hpp b/toml/lexer.hpp
index 95c9051..978dc5f 100644
--- a/toml/lexer.hpp
+++ b/toml/lexer.hpp
@@ -125,10 +125,17 @@ using lex_local_time       = lex_partial_time;
 // ===========================================================================
 
 using lex_quotation_mark  = character<'"'>;
+#ifdef TOML11_USE_UNRELEASED_TOML_FEATURES
 using lex_basic_unescaped = exclude<either<in_range<0x00, 0x08>, // 0x09 (tab)
                                            in_range<0x0a, 0x1F>, // is allowed
                                            character<0x22>, character<0x5C>,
                                            character<0x7F>>>;
+#else
+using lex_basic_unescaped = exclude<either<in_range<0x00, 0x1F>,
+                                           character<0x22>, character<0x5C>,
+                                           character<0x7F>>>;
+
+#endif
 using lex_escape          = character<'\\'>;
 using lex_escape_unicode_short = sequence<character<'u'>,
                                           repeat<lex_hex_dig, exactly<4>>>;
@@ -148,11 +155,18 @@ using lex_basic_string = sequence<lex_quotation_mark,
                                   lex_quotation_mark>;
 
 using lex_ml_basic_string_delim = repeat<lex_quotation_mark, exactly<3>>;
+#ifdef TOML11_USE_UNRELEASED_TOML_FEATURES
 using lex_ml_basic_unescaped    = exclude<either<in_range<0x00, 0x08>, // 0x09
                                                  in_range<0x0a, 0x1F>, // is tab
                                                  character<0x5C>,
                                                  character<0x7F>,
                                                  lex_ml_basic_string_delim>>;
+#else // TOML v0.5.0
+using lex_ml_basic_unescaped    = exclude<either<in_range<0x00,0x1F>,
+                                                 character<0x5C>,
+                                                 character<0x7F>,
+                                                 lex_ml_basic_string_delim>>;
+#endif
 
 using lex_ml_basic_escaped_newline = sequence<
         lex_escape, maybe<lex_ws>, lex_newline,