diff --git a/scripts/upgrade b/scripts/upgrade
index c9a46d7..332de9b 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -36,16 +36,32 @@ logs_path="/var/log/$app"
 #=================================================
 
 # Backup the current version of the app
-ynh_backup_before_upgrade
+# (NB: `tee` uses process substitution rather than a pipe,
+# to avoid spawning a subshell that would not save global
+# variables defined by `ynh_backup_before_upgrade`.)
+ynh_backup_before_upgrade > >(tee "upgrade.log")
+# Ensure the backup can be restored
+if grep -q "mattermost: Warning$" "upgrade.log"; then
+  can_restore_backup=false
+else
+  can_restore_backup=true
+fi
 
 # If the upgrade fails…
 ynh_clean_setup () {
-  # Stop attempting to restart the app
-  if $(sudo systemctl -q is-active "$app"); then
-    sudo systemctl stop "$app"
+  if [ "$can_restore_backup" = true ]; then
+    # Stop attempting to restart the app
+    if $(sudo systemctl -q is-active "$app"); then
+      sudo systemctl stop "$app"
+    fi
+    # Restore the backup
+    ynh_restore_upgradebackup
+  
+  else
+    # Backup restoration is not available:
+    # let's try at least to restart the server.
+    sudo systemctl start "$app"
   fi
-  # Restore the backup
-  ynh_restore_upgradebackup
 }
 
 # Exit if an error occurs during the execution of the script