diff --git a/ChangeLog b/ChangeLog
index 9c4c06408..143adae39 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -40,6 +40,7 @@ Bugfix
      smaller than the hash length. (Closes ticket #41)
    * If certificate serial is longer than 32 octets, serial number is now
      appended with '....' after first 28 octets
+   * Improved build support for s390x and sparc64 in bignum.h
 
 = Version 1.0.0 released on 2011-07-27
 Features
diff --git a/include/polarssl/bignum.h b/include/polarssl/bignum.h
index 2b8e82314..13085570d 100644
--- a/include/polarssl/bignum.h
+++ b/include/polarssl/bignum.h
@@ -86,7 +86,9 @@ typedef unsigned long  t_udbl;
   #else
     #if defined(__amd64__) || defined(__x86_64__)    || \
         defined(__ppc64__) || defined(__powerpc64__) || \
-        defined(__ia64__)  || defined(__alpha__)
+        defined(__ia64__)  || defined(__alpha__)     || \
+        (defined(__sparc__) && defined(__arch64__))  || \
+        defined(__s390x__)
     typedef unsigned int t_udbl __attribute__((mode(TI)));
     #else
       #if defined(POLARSSL_HAVE_LONGLONG)