diff -Nru autoconf-2.69/debian/changelog autoconf-2.69/debian/changelog
--- autoconf-2.69/debian/changelog	2014-02-23 16:29:25.000000000 +0000
+++ autoconf-2.69/debian/changelog	2014-03-27 21:48:37.000000000 +0000
@@ -1,3 +1,12 @@
+autoconf (2.69-6) unstable; urgency=low
+
+  * lib/autoconf/specific.m4: Use ((off_t) 1 << 31) << 31 in place of
+    (off_t) 1 << 62 to avoid undefined behavior when off_t is 32-bit.
+    Closes: #742780.  Thanks to Mathieu Malaterre <malat@debian.org> for
+    reporting this bug.
+
+ -- Ben Pfaff <pfaffben@debian.org>  Thu, 27 Mar 2014 14:48:36 -0700
+
 autoconf (2.69-5) unstable; urgency=low
 
   * debian/rules: Use upstream manpages instead of Debian-specific ones.
diff -Nru autoconf-2.69/debian/patches/avoid-undefined-behavior-for-32bit-off_t.patch autoconf-2.69/debian/patches/avoid-undefined-behavior-for-32bit-off_t.patch
--- autoconf-2.69/debian/patches/avoid-undefined-behavior-for-32bit-off_t.patch	1970-01-01 00:00:00.000000000 +0000
+++ autoconf-2.69/debian/patches/avoid-undefined-behavior-for-32bit-off_t.patch	2014-03-27 21:54:10.000000000 +0000
@@ -0,0 +1,26 @@
+Description: Fix undefined behavior for 32-bit off_t.
+ autoconf (2.69-6) unstable; urgency=low
+ .
+   * lib/autoconf/specific.m4: Use ((off_t) 1 << 31) << 31 in place of
+     (off_t) 1 << 62 to avoid undefined behavior when off_t is 32-bit.
+     Closes: #742780.  Thanks to Mathieu Malaterre <malat@debian.org> for
+     reporting this bug.
+Author: Ben Pfaff <pfaffben@debian.org>
+Bug-Debian: http://bugs.debian.org/742780
+
+---
+Bug: #742780.
+Bug-Debian: http://bugs.debian.org/742780
+Last-Update: 2014-03-27
+
+--- autoconf-2.69.orig/lib/autoconf/specific.m4
++++ autoconf-2.69/lib/autoconf/specific.m4
+@@ -92,7 +92,7 @@ m4_define([_AC_SYS_LARGEFILE_TEST_INCLUD
+     We can't simply define LARGE_OFF_T to be 9223372036854775807,
+     since some C++ compilers masquerading as C compilers
+     incorrectly reject 9223372036854775807.  */
+-@%:@define LARGE_OFF_T (((off_t) 1 << 62) - 1 + ((off_t) 1 << 62))
++@%:@define LARGE_OFF_T ((((off_t) 1 << 31) << 31) - 1 + (((off_t) 1 << 31) << 31))
+   int off_t_is_large[[(LARGE_OFF_T % 2147483629 == 721
+ 		       && LARGE_OFF_T % 2147483647 == 1)
+ 		      ? 1 : -1]];[]dnl
diff -Nru autoconf-2.69/debian/patches/series autoconf-2.69/debian/patches/series
--- autoconf-2.69/debian/patches/series	2013-08-11 17:49:20.000000000 +0000
+++ autoconf-2.69/debian/patches/series	2014-03-27 21:54:54.000000000 +0000
@@ -1,3 +1,4 @@
 atomic.patch
 stricter-versioning.patch
 texinfo.patch
+avoid-undefined-behavior-for-32bit-off_t.patch