diff --git a/mptcp/files/usr/share/omr/post-tracking.d/post-tracking b/mptcp/files/usr/share/omr/post-tracking.d/post-tracking
index 75a5b41ce..927a2853f 100755
--- a/mptcp/files/usr/share/omr/post-tracking.d/post-tracking
+++ b/mptcp/files/usr/share/omr/post-tracking.d/post-tracking
@@ -86,9 +86,17 @@ set_routes_intf() {
 				weight=1
 			fi
 			if [ "$multipath_config_route" = "backup" ]; then
-				routesintfbackup="$routesintf nexthop via $interface_gw dev $interface_if weight $weight"
+				if [ -z "$routesintfbackup" ]; then
+					routesintfbackup="nexthop via $interface_gw dev $interface_if weight $weight"
+				else
+					routesintfbackup="$routesintfbackup nexthop via $interface_gw dev $interface_if weight $weight"
+				fi
 			else
-				routesintf="$routesintf nexthop via $interface_gw dev $interface_if weight $weight"
+				if [ -z "$routesintf" ]; then
+					routesintf="nexthop via $interface_gw dev $interface_if weight $weight"
+				else
+					routesintf="$routesintf nexthop via $interface_gw dev $interface_if weight $weight"
+				fi
 			fi
 		fi
 	fi