diff --git a/mpi/mpi-internal.h b/mpi/mpi-internal.h
index c1df30ad8..46da08d0d 100644
--- a/mpi/mpi-internal.h
+++ b/mpi/mpi-internal.h
@@ -104,7 +104,7 @@ typedef int mpi_size_t;        /* (must be a signed type) */
     do {				\
 	mpi_size_t _i;			\
 	for( _i = 0; _i < (n); _i++ )	\
-	    (d)[_i] = (d)[_i];		\
+	    (d)[_i] = (s)[_i];		\
     } while (0)
 
 #define MPN_COPY_DECR( d, s, n ) \