diff --git a/debian/ngcp-kamailio.preinst b/debian/ngcp-kamailio.preinst
index 2ba0c4174..8623441d4 100644
--- a/debian/ngcp-kamailio.preinst
+++ b/debian/ngcp-kamailio.preinst
@@ -22,6 +22,15 @@ case "$1" in
                 fi
                 echo "Please take a look at kamailio.README.debian about how to upgrade your configuration."
             fi
+        elif dpkg --compare-versions "$2" "<" "4.1.0"; then
+            # sync_branch is obsolete
+            if [ -f /etc/default/kamailio.lb ]; then
+                sed -e 's/RUN_KAMAILIO=yes/RUN_KAMAILIO=no/' -i /etc/default/kamailio.lb
+            fi
+            if [ -f /etc/default/kamailio.proxy ]; then
+                sed -e 's/RUN_KAMAILIO=yes/RUN_KAMAILIO=no/' -i /etc/default/kamailio.proxy
+            fi
+            echo "kamailio deactivate. Run ngcpcfg apply to reactivate."
         fi
         ;;