diff -Nur mdadm-3.2.1.orig/Monitor.c mdadm-3.2.1/Monitor.c
--- mdadm-3.2.1.orig/Monitor.c	2011-03-28 13:31:20.000000000 +1100
+++ mdadm-3.2.1/Monitor.c	2011-04-12 18:18:40.411908655 +1000
@@ -577,7 +577,8 @@
 			info[i].major = info[i].minor = 0;
 	}
 
-	if (strncmp(mse->metadata_version, "external:", 9) == 0 &&
+	if (mse->metadata_version &&
+	    strncmp(mse->metadata_version, "external:", 9) == 0 &&
 	    is_subarray(mse->metadata_version+9))
 		st->parent_dev =
 			devname2devnum(mse->metadata_version+10);
@@ -688,7 +689,8 @@
 			st->devnum = mse->devnum;
 			st->percent = -2;
 			st->expected_spares = -1;
-			if (strncmp(mse->metadata_version, "external:", 9) == 0 &&
+			if (mse->metadata_version &&
+			    strncmp(mse->metadata_version, "external:", 9) == 0 &&
 			    is_subarray(mse->metadata_version+9))
 				st->parent_dev =
 					devname2devnum(mse->metadata_version+10);