Index: memcached.c
===================================================================
--- memcached.c	(revision 606)
+++ memcached.c	(working copy)
@@ -1201,9 +1201,9 @@
 }
 
 static void process_arithmetic_command(conn *c, token_t *tokens, const size_t ntokens, const int incr) {
-    char temp[32];
+    char temp[sizeof("18446744073709551615")];
     item *it;
-    unsigned int delta;
+    uint64_t delta;
     char *key;
     size_t nkey;
 
@@ -1230,7 +1230,7 @@
         }
     }
 
-    delta = strtoul(tokens[2].value, NULL, 10);
+    delta = strtoull(tokens[2].value, NULL, 10);
 
     if(errno == ERANGE) {
         out_string(c, "CLIENT_ERROR bad command line format");
@@ -1257,15 +1257,15 @@
  *
  * returns a response string to send back to the client.
  */
-char *do_add_delta(item *it, const int incr, unsigned int delta, char *buf) {
+char *do_add_delta(item *it, const int incr, const uint64_t delta, char *buf) {
     char *ptr;
-    unsigned int value;
+    uint64_t value;
     int res;
 
     ptr = ITEM_data(it);
     while ((*ptr != '\0') && (*ptr < '0' && *ptr > '9')) ptr++;    // BUG: can't be true
 
-    value = strtol(ptr, NULL, 10);
+    value = strtoull(ptr, NULL, 10);
 
     if(errno == ERANGE) {
         return "CLIENT_ERROR cannot increment or decrement non-numeric value";
@@ -1277,7 +1277,7 @@
         if (delta >= value) value = 0;
         else value -= delta;
     }
-    snprintf(buf, 32, "%u", value);
+    sprintf(buf, "%llu", value);
     res = strlen(buf);
     if (res + 2 > it->nbytes) { /* need to realloc */
         item *new_it;
Index: thread.c
===================================================================
--- thread.c	(revision 606)
+++ thread.c	(working copy)
@@ -462,7 +462,7 @@
 /*
  * Does arithmetic on a numeric item value.
  */
-char *mt_add_delta(item *item, int incr, unsigned int delta, char *buf) {
+char *mt_add_delta(item *item, int incr, const uint64_t delta, char *buf) {
     char *ret;
 
     pthread_mutex_lock(&cache_lock);
Index: memcached.h
===================================================================
--- memcached.h	(revision 606)
+++ memcached.h	(working copy)
@@ -222,7 +222,7 @@
 bool do_conn_add_to_freelist(conn *c);
 char *do_defer_delete(item *item, time_t exptime);
 void do_run_deferred_deletes(void);
-char *do_add_delta(item *item, int incr, const unsigned int delta, char *buf);
+char *do_add_delta(item *item, int incr, const uint64_t delta, char *buf);
 int do_store_item(item *item, int comm);
 conn *conn_new(const int sfd, const int init_state, const int event_flags, const int read_buffer_size, const bool is_udp, struct event_base *base);
 
@@ -253,7 +253,7 @@
 void dispatch_conn_new(int sfd, int init_state, int event_flags, int read_buffer_size, int is_udp);
 
 /* Lock wrappers for cache functions that are called from main loop. */
-char *mt_add_delta(item *item, const int incr, const unsigned int delta, char *buf);
+char *mt_add_delta(item *item, const int incr, const uint64_t delta, char *buf);
 void mt_assoc_move_next_bucket(void);
 conn *mt_conn_from_freelist(void);
 bool  mt_conn_add_to_freelist(conn *c);
Index: t/incrdecr.t
===================================================================
--- t/incrdecr.t	(revision 606)
+++ t/incrdecr.t	(working copy)
@@ -1,7 +1,7 @@
 #!/usr/bin/perl
 
 use strict;
-use Test::More tests => 13;
+use Test::More tests => 17;
 use FindBin qw($Bin);
 use lib "$Bin/lib";
 use MemcachedTest;
@@ -30,6 +30,18 @@
 print $sock "decr num 5\r\n";
 is(scalar <$sock>, "0\r\n", "- 5 = 0");
 
+printf $sock "set num 0 0 10\r\n4294967296\r\n";
+is(scalar <$sock>, "STORED\r\n", "stored 2**32");
+
+print $sock "incr num 1\r\n";
+is(scalar <$sock>, "4294967297\r\n", "4294967296 + 1 = 4294967297");
+
+printf $sock "set num 0 0 %d\r\n18446744073709551615\r\n", length("18446744073709551615");
+is(scalar <$sock>, "STORED\r\n", "stored 2**64-1");
+
+print $sock "incr num 1\r\n";
+is(scalar <$sock>, "0\r\n", "(2**64 - 1) + 1 = 0");
+
 print $sock "decr bogus 5\r\n";
 is(scalar <$sock>, "NOT_FOUND\r\n", "can't decr bogus key");
 
Index: doc/protocol.txt
===================================================================
--- doc/protocol.txt	(revision 606)
+++ doc/protocol.txt	(working copy)
@@ -252,7 +252,7 @@
 
 Commands "incr" and "decr" are used to change data for some item
 in-place, incrementing or decrementing it. The data for the item is
-treated as decimal representation of a 32-bit unsigned integer. If the
+treated as decimal representation of a 64-bit unsigned integer. If the
 current data value does not conform to such a representation, the
 commands behave as if the value were 0. Also, the item must already
 exist for incr/decr to work; these commands won't pretend that a
@@ -269,7 +269,7 @@
 - <key> is the key of the item the client wishes to change
 
 - <value> is the amount by which the client wants to increase/decrease
-the item. It is a decimal representation of a 32-bit unsigned integer.
+the item. It is a decimal representation of a 64-bit unsigned integer.
 
 The response will be one of:
 
@@ -280,7 +280,7 @@
 
 Note that underflow in the "decr" command is caught: if a client tries
 to decrease the value below 0, the new value will be 0. Overflow in
-the "incr" command is not checked.
+the "incr" command will wrap around the 64 bit mark.
 
 Note also that decrementing a number such that it loses length isn't
 guaranteed to decrement its returned length.  The number MAY be