diff --git a/pkgs/tools/text/mairix/default.nix b/pkgs/tools/text/mairix/default.nix
index f3fece1f177..d8db034f151 100644
--- a/pkgs/tools/text/mairix/default.nix
+++ b/pkgs/tools/text/mairix/default.nix
@@ -10,9 +10,10 @@ stdenv.mkDerivation rec {
 
   buildInputs = [ zlib bzip2 bison flex ];
 
-  # https://github.com/rc0/mairix/issues/12
+  # https://github.com/rc0/mairix/pull/19
   patches = [ ./mmap.patch ];
-  patchFlags = "-p2";
+
+  enableParallelBuilding = true;
 
   meta = {
     homepage = http://www.rc0.org.uk/mairix;
diff --git a/pkgs/tools/text/mairix/mmap.patch b/pkgs/tools/text/mairix/mmap.patch
index 0d43ac7ce7a..241083f2dde 100644
--- a/pkgs/tools/text/mairix/mmap.patch
+++ b/pkgs/tools/text/mairix/mmap.patch
@@ -1,25 +1,29 @@
-Fix "Cannot allocate memory" on mmap of files bigger than 2GiB.
+Making mairix work with mbox files over 2GB.
 
-https://github.com/rc0/mairix/issues/12
+https://github.com/rc0/mairix/pull/19
 
-diff -ruN t/mairix-0.22/mairix.h mairix/mairix-0.22/mairix.h
---- t/mairix-0.22/mairix.h  2010-06-05 14:41:10.000000000 -0700
-+++ mairix/mairix-0.22/mairix.h 2015-07-08 13:33:06.678718524 -0700
-@@ -327,8 +327,8 @@
+diff --git a/mairix.h b/mairix.h
+index 2480492..cb25824 100644
+--- a/mairix.h
++++ b/mairix.h
+@@ -327,9 +327,9 @@ enum data_to_rfc822_error {
+   DTR8_BAD_HEADERS, /* corrupt headers */
    DTR8_BAD_ATTACHMENT /* corrupt attachment (e.g. no body part) */
  };
- struct rfc822 *data_to_rfc822(struct msg_src *src, char *data, int length, enum data_to_rfc822_error *error);
+-struct rfc822 *data_to_rfc822(struct msg_src *src, char *data, int length, enum data_to_rfc822_error *error);
 -void create_ro_mapping(const char *filename, unsigned char **data, int *len);
 -void free_ro_mapping(unsigned char *data, int len);
++struct rfc822 *data_to_rfc822(struct msg_src *src, char *data, size_t length, enum data_to_rfc822_error *error);
 +void create_ro_mapping(const char *filename, unsigned char **data, size_t *len);
 +void free_ro_mapping(unsigned char *data, size_t len);
  char *format_msg_src(struct msg_src *src);
-
+ 
  /* In tok.c */
-diff -ruN t/mairix-0.22/mbox.c mairix/mairix-0.22/mbox.c
---- t/mairix-0.22/mbox.c    2010-06-05 14:41:10.000000000 -0700
-+++ mairix/mairix-0.22/mbox.c   2015-07-08 13:32:45.126280861 -0700
-@@ -816,7 +816,7 @@
+diff --git a/mbox.c b/mbox.c
+index ebbfa78..396e27d 100644
+--- a/mbox.c
++++ b/mbox.c
+@@ -816,7 +816,7 @@ void build_mbox_lists(struct database *db, const char *folder_base, /*{{{*/
          mb->n_old_msgs_valid = mb->n_msgs;
        } else {
          unsigned char *va;
@@ -28,28 +32,65 @@ diff -ruN t/mairix-0.22/mbox.c mairix/mairix-0.22/mbox.c
          create_ro_mapping(mb->path, &va, &len);
          if (va) {
            rescan_mbox(mb, (char *) va, len);
-@@ -852,7 +852,7 @@
+@@ -852,7 +852,7 @@ int add_mbox_messages(struct database *db)/*{{{*/
    int any_new = 0;
    int N;
    unsigned char *va;
 -  int valen;
 +  size_t valen;
    enum data_to_rfc822_error error;
-
+ 
    for (i=0; i<db->n_mboxen; i++) {
-diff -ruN t/mairix-0.22/rfc822.c mairix/mairix-0.22/rfc822.c
---- t/mairix-0.22/rfc822.c  2010-06-05 14:41:10.000000000 -0700
-+++ mairix/mairix-0.22/rfc822.c 2015-07-08 13:30:59.388133879 -0700
-@@ -1250,7 +1250,7 @@
+diff --git a/reader.c b/reader.c
+index 71ac5bd..18f0108 100644
+--- a/reader.c
++++ b/reader.c
+@@ -81,7 +81,8 @@ static void read_toktable2_db(char *data, struct toktable2_db *toktable, int sta
+ /*}}}*/
+ struct read_db *open_db(char *filename)/*{{{*/
+ {
+-  int fd, len;
++  int fd;
++  size_t len;
+   char *data;
+   struct stat sb;
+   struct read_db *result;
+diff --git a/reader.h b/reader.h
+index 9b5dfa3..d709cc4 100644
+--- a/reader.h
++++ b/reader.h
+@@ -138,7 +138,7 @@ struct toktable2_db {/*{{{*/
+ struct read_db {/*{{{*/
+   /* Raw file parameters, needed later for munmap */
+   char *data;
+-  int len;
++  size_t len;
+ 
+   /* Pathname information */
+   int n_msgs;
+diff --git a/rfc822.c b/rfc822.c
+index b411f85..9c8e1a4 100644
+--- a/rfc822.c
++++ b/rfc822.c
+@@ -990,7 +990,7 @@ static void scan_status_flags(const char *s, struct headers *hdrs)/*{{{*/
+ 
+ /*{{{ data_to_rfc822() */
+ struct rfc822 *data_to_rfc822(struct msg_src *src,
+-    char *data, int length,
++    char *data, size_t length,
+     enum data_to_rfc822_error *error)
+ {
+   struct rfc822 *result;
+@@ -1265,7 +1265,7 @@ static struct ro_mapping *add_ro_cache(const char *filename, int fd, size_t len)
  }
  #endif /* USE_GZIP_MBOX || USE_BZIP_MBOX */
-
+ 
 -void create_ro_mapping(const char *filename, unsigned char **data, int *len)/*{{{*/
 +void create_ro_mapping(const char *filename, unsigned char **data, size_t *len)/*{{{*/
  {
    struct stat sb;
    int fd;
-@@ -1371,7 +1371,7 @@
+@@ -1386,7 +1386,7 @@ comp_error:
    data_alloc_type = ALLOC_MMAP;
  }
  /*}}}*/
@@ -57,8 +98,8 @@ diff -ruN t/mairix-0.22/rfc822.c mairix/mairix-0.22/rfc822.c
 +void free_ro_mapping(unsigned char *data, size_t len)/*{{{*/
  {
    int r;
-
-@@ -1399,7 +1399,7 @@
+ 
+@@ -1414,7 +1414,7 @@ static struct msg_src *setup_msg_src(char *filename)/*{{{*/
  /*}}}*/
  struct rfc822 *make_rfc822(char *filename)/*{{{*/
  {
@@ -66,11 +107,12 @@ diff -ruN t/mairix-0.22/rfc822.c mairix/mairix-0.22/rfc822.c
 +  size_t len;
    unsigned char *data;
    struct rfc822 *result;
-
-diff -ruN t/mairix-0.22/search.c mairix/mairix-0.22/search.c
---- t/mairix-0.22/search.c  2010-06-05 14:41:10.000000000 -0700
-+++ mairix/mairix-0.22/search.c 2015-07-08 13:32:25.809888610 -0700
-@@ -667,7 +667,7 @@
+ 
+diff --git a/search.c b/search.c
+index 18b51ee..97967bc 100644
+--- a/search.c
++++ b/search.c
+@@ -681,7 +681,7 @@ static void mbox_terminate(const unsigned char *data, int len, FILE *out)/*{{{*/
  static void append_file_to_mbox(const char *path, FILE *out)/*{{{*/
  {
    unsigned char *data;
@@ -79,8 +121,8 @@ diff -ruN t/mairix-0.22/search.c mairix/mairix-0.22/search.c
    create_ro_mapping(path, &data, &len);
    if (data) {
      fprintf(out, "From mairix@mairix Mon Jan  1 12:34:56 1970\n");
-@@ -683,8 +683,8 @@
-
+@@ -698,8 +698,8 @@ static int had_failed_checksum;
+ 
  static void get_validated_mbox_msg(struct read_db *db, int msg_index,/*{{{*/
                                     int *mbox_index,
 -                                   unsigned char **mbox_data, int *mbox_len,
@@ -90,16 +132,16 @@ diff -ruN t/mairix-0.22/search.c mairix/mairix-0.22/search.c
  {
    /* msg_data==NULL if checksum mismatches */
    unsigned char *start;
-@@ -715,7 +715,7 @@
+@@ -738,7 +738,7 @@ static void append_mboxmsg_to_mbox(struct read_db *db, int msg_index, FILE *out)
  {
    /* Need to common up code with try_copy_to_path */
    unsigned char *mbox_start, *msg_start;
 -  int mbox_len, msg_len;
 +  size_t mbox_len, msg_len;
    int mbox_index;
-
+ 
    get_validated_mbox_msg(db, msg_index, &mbox_index, &mbox_start, &mbox_len, &msg_start, &msg_len);
-@@ -735,7 +735,7 @@
+@@ -759,7 +759,7 @@ static void append_mboxmsg_to_mbox(struct read_db *db, int msg_index, FILE *out)
  static void try_copy_to_path(struct read_db *db, int msg_index, char *target_path)/*{{{*/
  {
    unsigned char *data;
@@ -108,3 +150,12 @@ diff -ruN t/mairix-0.22/search.c mairix/mairix-0.22/search.c
    int mbi;
    FILE *out;
    unsigned char *start;
+@@ -1214,7 +1214,7 @@ static int do_search(struct read_db *db, char **args, char *output_path, int sho
+                 unsigned int mbix, msgix;
+                 int start, len, after_end;
+                 unsigned char *mbox_start, *msg_start;
+-                int mbox_len, msg_len;
++                size_t mbox_len, msg_len;
+                 int mbox_index;
+ 
+                 start = db->mtime_table[i];