diff --git a/acconfig.h b/acconfig.h
index e87197fb..1e1bb19c 100644
--- a/acconfig.h
+++ b/acconfig.h
@@ -39,3 +39,14 @@
 
 /* SSL */
 #undef HAVE_OPENSSL
+
+/* If set to 64, enables 64bit off_t for some systems (eg. Linux, Solaris) */
+#undef _FILE_OFFSET_BITS
+
+/* What type should be used for uoff_t */
+#undef UOFF_T_INT
+#undef UOFF_T_LONG
+#undef UOFF_T_LONG_LONG
+
+/* printf()-format for uoff_t, eg. "u" or "lu" or "llu" */
+#undef PRIuUOFF_T
diff --git a/configure.in b/configure.in
index 45667592..e2160369 100644
--- a/configure.in
+++ b/configure.in
@@ -183,6 +183,12 @@ AC_ARG_WITH(perl,
 	fi,
 	want_perl=static)
 
+AC_ARG_WITH(file-offset-size,
+[  --with-file-offset-size=BITS  Set size of file offsets. Usually 32 or 64.
+                          (default: 64 if available)],
+	preferred_off_t_bits=$withval,
+	preferred_off_t_bits=64)
+
 AC_ARG_ENABLE(ipv6,
 [  --enable-ipv6           Enable IPv6 support],
 	if test x$enableval = xyes; then
@@ -262,6 +268,54 @@ AC_DEFINE(socklen_t, int, Define to 'int' if <sys/socket.h> doesn't define.)
 fi
 AC_MSG_RESULT($irssi_cv_type_socklen_t)
 
+dnl * off_t checks, try to make it 64bit
+AC_DEFINE_UNQUOTED(_FILE_OFFSET_BITS, $preferred_off_t_bits)
+
+AC_CHECK_SIZEOF(int)
+AC_CHECK_SIZEOF(long)
+AC_CHECK_SIZEOF(long long)
+
+dnl * older autoconfs don't include sys/types.h, so do it manually
+AC_MSG_CHECKING([size of off_t])
+AC_TRY_RUN([
+  #include <stdio.h>
+  #include <sys/types.h>
+  int main() {
+    FILE *f=fopen("conftestval", "w");
+    if (!f) exit(1);
+    fprintf(f, "%d\n", sizeof(off_t));
+    return 0;
+  }
+], [
+  sizeof_off_t=`cat conftestval`
+  rm -f conftestval
+], [
+  AC_ERROR([Unsupported off_t size])
+])
+AC_MSG_RESULT($sizeof_off_t)
+
+if test $sizeof_off_t = 8; then
+  offt_64bit=yes
+else
+  offt_64bit=no
+fi
+
+if test x$sizeof_off_t = x$ac_cv_sizeof_long; then
+  # try to use unsigned long always first
+  AC_DEFINE_UNQUOTED(PRIuUOFF_T, "lu")
+  AC_DEFINE(UOFF_T_LONG)
+elif test x$sizeof_off_t = x$ac_cv_sizeof_int; then
+  # next try int
+  AC_DEFINE_UNQUOTED(PRIuUOFF_T, "u")
+  AC_DEFINE(UOFF_T_INT)
+elif test x$sizeof_off_t = x$ac_cv_sizeof_long_long; then
+  # and finally long long
+  AC_DEFINE_UNQUOTED(PRIuUOFF_T, "llu")
+  AC_DEFINE(UOFF_T_LONG_LONG)
+else
+  AC_ERROR([Couldn't find integer type for off_t])
+fi
+
 dnl **
 dnl ** check for socks
 dnl **
@@ -892,11 +946,11 @@ elif test "x$want_terminfo" = "xyes"; then
 else
 	text="yes, using curses"
 fi
-echo "Building text frontend ..... : $text"
-echo "Building irssi bot ......... : $want_irssibot"
-echo "Building irssi proxy ....... : $want_irssiproxy"
+echo "Building text frontend ........... : $text"
+echo "Building irssi bot ............... : $want_irssibot"
+echo "Building irssi proxy ............. : $want_irssiproxy"
 if test "x$have_gmodule" = "xyes"; then
-	echo "Building with module support : yes"
+	echo "Building with module support ..... : yes"
 else
 	echo "Building with module support : NO!! /LOAD will not work!"
 	echo " - You're missing gmodule (comes with glib) for some reason,"
@@ -904,14 +958,14 @@ else
 fi
 
 if test "x$want_perl" = "xstatic"; then
-	echo "Building with Perl support . : static (in irssi binary)"
+	echo "Building with Perl support ....... : static (in irssi binary)"
 elif test "x$want_perl" = "xmodule"; then
-	echo "Building with Perl support . : module"
+	echo "Building with Perl support ....... : module"
 else
 	if test -z "$perl_check_error"; then
-		echo "Building with Perl support . : no"
+		echo "Building with Perl support ....... : no"
 	else
-		echo "Building with Perl support . : NO!"
+		echo "Building with Perl support ....... : NO!"
 		echo " - $perl_check_error"
 	fi
 fi
@@ -933,7 +987,7 @@ if test "x$want_perl" != "xno"; then
 	if test -z "$perl_library_dir"; then
 		perl_library_dir="(site default - `$perlpath -e 'use Config; print $Config{sitearch}'`)"
 	fi
-       	echo "Perl library directory ..... : $perl_library_dir"
+       	echo "Perl library directory ........... : $perl_library_dir"
 	if test "x$perl_prefix_note" = "xyes"; then
 		echo "  - NOTE: This was automatically set to the same directory you gave with"
 		echo "  --prefix. If you want the perl libraries to install to their 'correct'"
@@ -941,12 +995,13 @@ if test "x$want_perl" != "xno"; then
 		echo "  Anyway, installing perl to this directory should work just as well."
 	fi
 fi
-echo "Install prefix ............. : $prefix"
+echo "Install prefix ................... : $prefix"
 
 echo
 
-echo "Building with IPv6 support . : $want_ipv6"
-echo "Building with SSL support .. : ${enable_openssl}"
+echo "Building with IPv6 support ....... : $want_ipv6"
+echo "Building with SSL support ........ : ${enable_openssl}"
+echo "Building with 64bit DCC support .. : $offt_64bit"
 if test "x$enable_openssl" = "xno" -a "x$ssl_error" != "x"; then
   echo "  - $ssl_error"
 fi
diff --git a/src/common.h b/src/common.h
index 95a49b2f..66af15cf 100644
--- a/src/common.h
+++ b/src/common.h
@@ -52,6 +52,16 @@
 #  include <gmodule.h>
 #endif
 
+#if defined (UOFF_T_INT)
+typedef unsigned int uoff_t;
+#elif defined (UOFF_T_LONG)
+typedef unsigned long uoff_t;
+#elif defined (UOFF_T_LONG_LONG)
+typedef unsigned long long uoff_t;
+#else
+#  error uoff_t size not set
+#endif
+
 /* input functions */
 #define G_INPUT_READ	(1 << 0)
 #define G_INPUT_WRITE	(1 << 1)
diff --git a/src/core/misc.c b/src/core/misc.c
index 886c40f1..00f9d096 100644
--- a/src/core/misc.c
+++ b/src/core/misc.c
@@ -592,6 +592,20 @@ int dec2octal(int decimal)
 	return octal;
 }
 
+/* string -> uoff_t */
+uoff_t str_to_uofft(const char *str)
+{
+	uoff_t ret;
+
+	ret = 0;
+	while (*str != '\0') {
+		ret = ret*10 + (*str - '0');
+		str++;
+	}
+
+	return ret;
+}
+
 /* convert all low-ascii (<32) to ^<A..> combinations */
 char *show_lowascii(const char *channel)
 {
diff --git a/src/core/misc.h b/src/core/misc.h
index b9002c1c..95946077 100644
--- a/src/core/misc.h
+++ b/src/core/misc.h
@@ -85,6 +85,9 @@ char *replace_chars(char *str, char from, char to);
 int octal2dec(int octal);
 int dec2octal(int decimal);
 
+/* string -> uoff_t */
+uoff_t str_to_uofft(const char *str);
+
 /* convert all low-ascii (<32) to ^<A..> combinations */
 char *show_lowascii(const char *channel);
 
diff --git a/src/irc/dcc/dcc-autoget.c b/src/irc/dcc/dcc-autoget.c
index 459f2a75..87dd00d8 100644
--- a/src/irc/dcc/dcc-autoget.c
+++ b/src/irc/dcc/dcc-autoget.c
@@ -58,7 +58,7 @@ static void sig_dcc_request(GET_DCC_REC *dcc, const char *nickaddr)
 	/* check file size limit, NOTE: it's still possible to send a
 	   bogus file size and then just send what ever sized file.. */
         max_size = settings_get_int("dcc_autoget_max_size");
-	if (max_size > 0 && (unsigned long) max_size*1024 < dcc->size)
+	if (max_size > 0 && (uoff_t)max_size*1024 < dcc->size)
                 return;
 
 	/* ok. but do we want/need to resume? */
diff --git a/src/irc/dcc/dcc-file-rec.h b/src/irc/dcc/dcc-file-rec.h
index a05dbc75..fe66a985 100644
--- a/src/irc/dcc/dcc-file-rec.h
+++ b/src/irc/dcc/dcc-file-rec.h
@@ -1,10 +1,9 @@
 #include "dcc-rec.h"
 
-unsigned long size, skipped; /* file size / skipped at start */
+uoff_t size, skipped; /* file size / skipped at start */
 int fhandle; /* file handle */
 int queue; /* queue number */
 
 /* counter buffer */
 char count_buf[4];
 int count_pos;
-
diff --git a/src/irc/dcc/dcc-get.c b/src/irc/dcc/dcc-get.c
index e8847698..9340645d 100644
--- a/src/irc/dcc/dcc-get.c
+++ b/src/irc/dcc/dcc-get.c
@@ -89,7 +89,7 @@ void dcc_get_send_received(GET_DCC_REC *dcc)
 {
 	guint32 recd;
 
-	recd = (guint32) htonl(dcc->transfd);
+	recd = (guint32) htonl(dcc->transfd & 0xffffffff);
 	memcpy(dcc->count_buf, &recd, 4);
 
 	dcc->count_pos =
@@ -133,7 +133,7 @@ static void sig_dccget_send(GET_DCC_REC *dcc)
 	}
 
 	memcpy(&recd, dcc->count_buf, 4);
-	if (recd != (guint32) htonl(dcc->transfd))
+	if (recd != (guint32) htonl(dcc->transfd & 0xffffffff))
                 dcc_get_send_received(dcc);
 }
 
@@ -323,7 +323,7 @@ static void ctcp_msg_dcc_send(IRC_SERVER_REC *server, const char *data,
 	char **params, *fname;
 	int paramcount, fileparams;
 	int port, len, quoted = FALSE;
-        long size;
+        uoff_t size;
 
 	/* SEND <file name> <address> <port> <size> [...] */
 	params = g_strsplit(data, " ", -1);
@@ -341,7 +341,7 @@ static void ctcp_msg_dcc_send(IRC_SERVER_REC *server, const char *data,
 	address = params[fileparams];
 	dcc_str2ip(address, &ip);
 	port = atoi(params[fileparams+1]);
-	size = atol(params[fileparams+2]);
+	size = str_to_uofft(params[fileparams+2]);
 
 	params[fileparams] = NULL;
         fname = g_strjoinv(" ", params);
diff --git a/src/irc/dcc/dcc-rec.h b/src/irc/dcc/dcc-rec.h
index 02cde37c..9fdd9582 100644
--- a/src/irc/dcc/dcc-rec.h
+++ b/src/irc/dcc/dcc-rec.h
@@ -18,7 +18,7 @@ int port; /* port we're connected in */
 GIOChannel *handle; /* socket handle */
 int tagconn, tagread, tagwrite;
 time_t starttime; /* transfer start time */
-unsigned long transfd; /* bytes transferred */
+uoff_t transfd; /* bytes transferred */
 
 unsigned int destroyed:1; /* We're about to destroy this DCC recond */
 
diff --git a/src/irc/dcc/dcc-resume.c b/src/irc/dcc/dcc-resume.c
index b273c54d..3cae3fa5 100644
--- a/src/irc/dcc/dcc-resume.c
+++ b/src/irc/dcc/dcc-resume.c
@@ -45,7 +45,7 @@ static FILE_DCC_REC *dcc_resume_find(int type, const char *nick, int port)
 }
 
 static int dcc_ctcp_resume_parse(int type, const char *data, const char *nick,
-				 FILE_DCC_REC **dcc, unsigned long *size)
+				 FILE_DCC_REC **dcc, uoff_t *size)
 {
 	char **params;
 	int paramcount;
@@ -57,7 +57,7 @@ static int dcc_ctcp_resume_parse(int type, const char *data, const char *nick,
 
 	if (paramcount >= 3) {
 		port = atoi(params[paramcount-2]);
-		*size = strtoul(params[paramcount-1], NULL, 10);
+		*size = str_to_uofft(params[paramcount-1]);
 
 		*dcc = dcc_resume_find(type, nick, port);
 	}
@@ -66,14 +66,14 @@ static int dcc_ctcp_resume_parse(int type, const char *data, const char *nick,
 }
 
 static int dcc_resume_file_check(FILE_DCC_REC *dcc, IRC_SERVER_REC *server,
-				 unsigned long size)
+				 uoff_t size)
 {
 	if (size >= dcc->size) {
 		/* whole file sent */
 		dcc->starttime = time(NULL);
 		dcc_reject(DCC(dcc), server);
-	} else if (lseek(dcc->fhandle, size, SEEK_SET) != (long)size) {
-		/* error, or trying to seek after end of file */
+	} else if (lseek(dcc->fhandle, (off_t)size, SEEK_SET) != (off_t)size) {
+		/* error */
 		dcc_reject(DCC(dcc), server);
 	} else {
 		dcc->transfd = dcc->skipped = size;
@@ -90,15 +90,15 @@ static void ctcp_msg_dcc_resume(IRC_SERVER_REC *server, const char *data,
 {
 	FILE_DCC_REC *dcc;
         char *str;
-        unsigned long size;
+        uoff_t size;
 
 	if (!dcc_ctcp_resume_parse(DCC_SEND_TYPE, data, nick, &dcc, &size)) {
 		signal_emit("dcc error ctcp", 5, "RESUME", data,
 			    nick, addr, target);
 	} else if (dcc != NULL && dcc_resume_file_check(dcc, server, size)) {
 		str = g_strdup_printf(DCC_SEND(dcc)->file_quoted ?
-				      "DCC ACCEPT \"%s\" %d %lu" :
-				      "DCC ACCEPT %s %d %lu",
+				      "DCC ACCEPT \"%s\" %d %"PRIuUOFF_T :
+				      "DCC ACCEPT %s %d %"PRIuUOFF_T,
 				      dcc->arg, dcc->port, dcc->transfd);
 		dcc_ctcp_message(dcc->server, dcc->nick,
 				 dcc->chat, FALSE, str);
@@ -112,7 +112,7 @@ static void ctcp_msg_dcc_accept(IRC_SERVER_REC *server, const char *data,
 				const char *target, DCC_REC *chat)
 {
 	FILE_DCC_REC *dcc;
-        unsigned long size;
+        uoff_t size;
 
 	if (!dcc_ctcp_resume_parse(DCC_GET_TYPE, data, nick, &dcc, &size) ||
 	    (dcc != NULL && DCC_GET(dcc)->get_type != DCC_GET_RESUME)) {
@@ -141,7 +141,7 @@ static void dcc_send_resume(GET_DCC_REC *dcc)
 	dcc->get_type = DCC_GET_RESUME;
 
 	pos = lseek(dcc->fhandle, 0, SEEK_END);
-	dcc->transfd = pos == (off_t)-1 ? 0 : (unsigned long) pos;
+	dcc->transfd = pos < 0 ? 0 : (uoff_t)pos;
 	dcc->skipped = dcc->transfd;
 
 	if (dcc->skipped == dcc->size) {
@@ -150,8 +150,8 @@ static void dcc_send_resume(GET_DCC_REC *dcc)
 		dcc_reject(DCC(dcc), NULL);
 	} else {
 		str = g_strdup_printf(dcc->file_quoted ?
-				      "DCC RESUME \"%s\" %d %lu" :
-				      "DCC RESUME %s %d %lu",
+				      "DCC RESUME \"%s\" %d %"PRIuUOFF_T :
+				      "DCC RESUME %s %d %"PRIuUOFF_T,
 				      dcc->arg, dcc->port, dcc->transfd);
 		dcc_ctcp_message(dcc->server, dcc->nick,
 				 dcc->chat, FALSE, str);
diff --git a/src/irc/dcc/dcc-send.c b/src/irc/dcc/dcc-send.c
index a75984ac..46e1dd4e 100644
--- a/src/irc/dcc/dcc-send.c
+++ b/src/irc/dcc/dcc-send.c
@@ -254,7 +254,6 @@ static void dcc_send_read_size(SEND_DCC_REC *dcc)
 	guint32 bytes;
 	int ret;
 
-	/* we need to get 4 bytes.. */
 	ret = net_receive(dcc->handle, dcc->count_buf+dcc->count_pos,
 			  4-dcc->count_pos);
 	if (ret == -1) {
@@ -267,14 +266,12 @@ static void dcc_send_read_size(SEND_DCC_REC *dcc)
 	if (dcc->count_pos != 4)
 		return;
 
-	memcpy(&bytes, dcc->count_buf, 4);
-	bytes = (guint32) ntohl(bytes);
-
-	dcc->gotalldata = (unsigned long) bytes == dcc->transfd;
+	bytes = ntohl(*((guint32 *) dcc->count_buf));
 	dcc->count_pos = 0;
 
-	if (dcc->waitforend && dcc->gotalldata) {
+	if (dcc->waitforend && bytes == (dcc->transfd & 0xffffffff)) {
 		/* file is sent */
+		dcc->gotalldata = TRUE;
 		dcc_close(DCC(dcc));
 	}
 }
@@ -334,10 +331,10 @@ static char *dcc_send_get_file(const char *fname)
 static int dcc_send_one_file(int queue, const char *target, const char *fname,
 			     IRC_SERVER_REC *server, CHAT_DCC_REC *chat)
 {
+	struct stat st;
 	char *str;
 	char host[MAX_IP_LEN];
 	int hfile, port;
-	long fsize;
         SEND_DCC_REC *dcc;
 	IPADDR own_ip;
         GIOChannel *handle;
@@ -356,8 +353,12 @@ static int dcc_send_one_file(int queue, const char *target, const char *fname,
 			    GINT_TO_POINTER(errno));
 		return FALSE;
 	}
-	fsize = lseek(hfile, 0, SEEK_END);
-	lseek(hfile, 0, SEEK_SET);
+
+	if (fstat(hfile, &st) < 0) {
+		g_warning("fstat() failed: %s", strerror(errno));
+		close(hfile);
+		return FALSE;
+	}
 
         /* start listening */
 	handle = dcc_listen(chat != NULL ? chat->handle :
@@ -386,7 +387,7 @@ static int dcc_send_one_file(int queue, const char *target, const char *fname,
 
 	dcc->handle = handle;
 	dcc->port = port;
-	dcc->size = fsize;
+	dcc->size = st.st_size;
 	dcc->fhandle = hfile;
 	dcc->queue = queue;
         dcc->file_quoted = strchr(fname, ' ') != NULL;
@@ -398,9 +399,9 @@ static int dcc_send_one_file(int queue, const char *target, const char *fname,
 
 	dcc_ip2str(&own_ip, host);
 	str = g_strdup_printf(dcc->file_quoted ?
-			      "DCC SEND \"%s\" %s %d %lu" :
-			      "DCC SEND %s %s %d %lu",
-			      dcc->arg, host, port, fsize);
+			      "DCC SEND \"%s\" %s %d %"PRIuUOFF_T :
+			      "DCC SEND %s %s %d %"PRIuUOFF_T,
+			      dcc->arg, host, port, dcc->size);
 	dcc_ctcp_message(server, target, chat, FALSE, str);
 	g_free(str);