diff --git a/http_parser.c b/http_parser.c
index ac511f6..6a6e4e9 100644
--- a/http_parser.c
+++ b/http_parser.c
@@ -133,6 +133,48 @@ static const char acceptable_header[256] = {
        'x',     'y',     'z',      0,       0,       0,       0,       0 };
 
 
+/* Tokens as defined by rfc 2616. Also lowercases them.
+ *        token       = 1*<any CHAR except CTLs or separators>
+ *     separators     = "(" | ")" | "<" | ">" | "@"
+ *                    | "," | ";" | ":" | "\" | <">
+ *                    | "/" | "[" | "]" | "?" | "="
+ *                    | "{" | "}" | SP | HT
+ */
+static const char tokens[256] = {
+/*   0 nul    1 soh    2 stx    3 etx    4 eot    5 enq    6 ack    7 bel  */
+        0,       0,       0,       0,       0,       0,       0,       0,
+/*   8 bs     9 ht    10 nl    11 vt    12 np    13 cr    14 so    15 si   */
+        0,       0,       0,       0,       0,       0,       0,       0,
+/*  16 dle   17 dc1   18 dc2   19 dc3   20 dc4   21 nak   22 syn   23 etb */
+        0,       0,       0,       0,       0,       0,       0,       0,
+/*  24 can   25 em    26 sub   27 esc   28 fs    29 gs    30 rs    31 us  */
+        0,       0,       0,       0,       0,       0,       0,       0,
+/*  32 sp    33  !    34  "    35  #    36  $    37  %    38  &    39  '  */
+       ' ',      '!',     '"',     '#',     '$',     '%',     '&',    '\'',
+/*  40  (    41  )    42  *    43  +    44  ,    45  -    46  .    47  /  */
+        0,       0,      '*',     '+',      0,      '-',     '.',     '/',
+/*  48  0    49  1    50  2    51  3    52  4    53  5    54  6    55  7  */
+       '0',     '1',     '2',     '3',     '4',     '5',     '6',     '7',
+/*  56  8    57  9    58  :    59  ;    60  <    61  =    62  >    63  ?  */
+       '8',     '9',      0,       0,       0,       0,       0,       0,
+/*  64  @    65  A    66  B    67  C    68  D    69  E    70  F    71  G  */
+        0,      'a',     'b',     'c',     'd',     'e',     'f',     'g',
+/*  72  H    73  I    74  J    75  K    76  L    77  M    78  N    79  O  */
+       'h',     'i',     'j',     'k',     'l',     'm',     'n',     'o',
+/*  80  P    81  Q    82  R    83  S    84  T    85  U    86  V    87  W  */
+       'p',     'q',     'r',     's',     't',     'u',     'v',     'w',
+/*  88  X    89  Y    90  Z    91  [    92  \    93  ]    94  ^    95  _  */
+       'x',     'y',     'z',      0,       0,       0,      '^',     '_',
+/*  96  `    97  a    98  b    99  c   100  d   101  e   102  f   103  g  */
+       '`',     'a',     'b',     'c',     'd',     'e',     'f',     'g',
+/* 104  h   105  i   106  j   107  k   108  l   109  m   110  n   111  o  */
+       'h',     'i',     'j',     'k',     'l',     'm',     'n',     'o',
+/* 112  p   113  q   114  r   115  s   116  t   117  u   118  v   119  w  */
+       'p',     'q',     'r',     's',     't',     'u',     'v',     'w',
+/* 120  x   121  y   122  z   123  {   124  |   125  }   126  ~   127 del */
+       'x',     'y',     'z',      0,      '|',     '}',     '~',       0 };
+
+
 static const int8_t unhex[256] =
   {-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1
   ,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1
@@ -292,6 +334,7 @@ enum flags
 #define CR '\r'
 #define LF '\n'
 #define LOWER(c) (unsigned char)(c | 0x20)
+#define TOKEN(c) tokens[(unsigned char)c]
 
 
 #define start_state (parser->type == HTTP_REQUEST ? s_start_req : s_start_res)
@@ -996,9 +1039,9 @@ size_t http_parser_execute (http_parser *parser,
           goto headers_almost_done;
         }
 
-        c = LOWER(ch);
+        c = TOKEN(ch);
 
-        if (c < 'a' || 'z' < c) goto error;
+        if (!c) goto error;
 
         MARK(header_field);
 
@@ -1031,7 +1074,7 @@ size_t http_parser_execute (http_parser *parser,
 
       case s_header_field:
       {
-        c = acceptable_header[(unsigned char)ch];
+        c = TOKEN(ch);
 
         if (c) {
           switch (header_state) {
diff --git a/test.c b/test.c
index af9f3bb..e3a12d8 100644
--- a/test.c
+++ b/test.c
@@ -31,7 +31,7 @@
 #undef FALSE
 #define FALSE 0
 
-#define MAX_HEADERS 10
+#define MAX_HEADERS 13
 #define MAX_ELEMENT_SIZE 500
 
 #define MIN(a,b) ((a) < (b) ? (a) : (b))
@@ -833,6 +833,47 @@ const struct message responses[] =
   ,.body= "<xml>hello</xml>"
   }
 
+
+#define RES_FIELD_UNDERSCORE 10
+/* Should handle spaces in header fields */
+, {.name= "field underscore"
+  ,.type= HTTP_RESPONSE
+  ,.raw= "HTTP/1.1 200 OK\r\n"
+         "Date: Tue, 28 Sep 2010 01:14:13 GMT\r\n"
+         "Server: Apache\r\n"
+         "Cache-Control: no-cache, must-revalidate\r\n"
+         "Expires: Mon, 26 Jul 1997 05:00:00 GMT\r\n"
+         "Set-Cookie: PlaxoCS=1274804622353690521; path=/; domain=.plaxo.com\r\n"
+         "Vary: Accept-Encoding\r\n"
+         "_eep-Alive: timeout=45\r\n" /* semantic value ignored */
+         "_onnection: Keep-Alive\r\n" /* semantic value ignored */
+         "Transfer-Encoding: chunked\r\n"
+         "Content-Type: text/html\r\n"
+         "Connection: close\r\n"
+         "\r\n"
+         "0\r\n\r\n"
+  ,.should_keep_alive= FALSE
+  ,.message_complete_on_eof= FALSE
+  ,.http_major= 1
+  ,.http_minor= 1
+  ,.status_code= 200
+  ,.num_headers= 11
+  ,.headers=
+    { { "Date", "Tue, 28 Sep 2010 01:14:13 GMT" }
+    , { "Server", "Apache" }
+    , { "Cache-Control", "no-cache, must-revalidate" }
+    , { "Expires", "Mon, 26 Jul 1997 05:00:00 GMT" }
+    , { "Set-Cookie", "PlaxoCS=1274804622353690521; path=/; domain=.plaxo.com" }
+    , { "Vary", "Accept-Encoding" }
+    , { "_eep-Alive", "timeout=45" }
+    , { "_onnection", "Keep-Alive" }
+    , { "Transfer-Encoding", "chunked" }
+    , { "Content-Type", "text/html" }
+    , { "Connection", "close" }
+    }
+  ,.body= ""
+  }
+
 , {.name= NULL } /* sentinel */
 };