diff --git a/archiver/isomaster/isomaster.conf b/archiver/isomaster/isomaster.conf
index 3ecc90160..2f3157056 100644
--- a/archiver/isomaster/isomaster.conf
+++ b/archiver/isomaster/isomaster.conf
@@ -12,4 +12,4 @@
 # GNU General Public License can be found in the file COPYING.
 # --- SDE-COPYRIGHT-NOTE-END ---
 runconf=0
-var_append makeinstopt PREFIX=$root/$prefix
+var_append makeinstopt " " "PREFIX=$root/$prefix"