diff --git a/tests/env-ddf-template b/tests/env-ddf-template
index c0a4b71..90d7272 100644
--- a/tests/env-ddf-template
+++ b/tests/env-ddf-template
@@ -4,7 +4,7 @@ sha1_sum() {
 
 get_rootdev() {
     local dev=$(stat -c %D /)
-    local maj=$(expr $dev : '\(..\)')
+    local maj=$(expr $dev : '\(..*\)..')
     local min=${dev#$maj}
     local bd=/dev/$(basename $(readlink /sys/dev/block/$((0x$maj)):$((0x$min))))
     [ -b $bd ] || exit 1