Index: mpi-1.8.6/mpi.h
===================================================================
--- mpi-1.8.6.orig/mpi.h	2011-12-13 09:35:31.000000000 -0800
+++ mpi-1.8.6/mpi.h	2011-12-13 09:40:01.000000000 -0800
@@ -72,8 +72,13 @@
 #define MAX_RADIX         64
 
 typedef struct {
-  mp_sign       sign;    /* sign of this quantity      */
-  mp_size       alloc;   /* how many digits allocated  */
+#if SIZEOF_INT >= SIZEOF_PTR
+  unsigned int  sign : 1;                  /* sign of this quantity      */
+  unsigned int  alloc : sizeof(int) - 1;   /* how many digits allocated  */
+#else
+  mp_sign       sign;
+  mp_size       alloc;
+#endif
   mp_size       used;    /* how many digits used       */
   mp_digit     *dp;      /* the digits themselves      */
 } mp_int;