diff -urN mdadm-3.1.1.orig/Grow.c mdadm-3.1.1/Grow.c
--- mdadm-3.1.1.orig/Grow.c	2009-11-19 06:13:29.000000000 +0100
+++ mdadm-3.1.1/Grow.c	2010-01-18 17:07:40.776572516 +0100
@@ -891,7 +891,7 @@
 		}
 
 		/* Check that we can hold all the data */
-		size = ndata * array.size;
+		size = ndata * (long long)array.size;
 		get_dev_size(fd, NULL, &array_size);
 		if (size < (array_size/1024)) {
 			fprintf(stderr, Name ": this change will reduce the size of the array.\n"