diff --git a/lib/tasks/migrate_from_mantis.rake b/lib/tasks/migrate_from_mantis.rake
index f07f4a306..9789438c3 100644
--- a/lib/tasks/migrate_from_mantis.rake
+++ b/lib/tasks/migrate_from_mantis.rake
@@ -22,6 +22,8 @@ require 'pp'
 
 namespace :redmine do
 task :migrate_from_mantis => :environment do
+  # TODO: Remove this unsupported Mantis migration task in a later version.
+  abort "This task is no longer maintained and cannot be used. It will be removed in a future version of Redmine."
 
   module MantisMigrate
 
diff --git a/lib/tasks/migrate_from_trac.rake b/lib/tasks/migrate_from_trac.rake
index c079d9061..330760351 100644
--- a/lib/tasks/migrate_from_trac.rake
+++ b/lib/tasks/migrate_from_trac.rake
@@ -21,6 +21,8 @@ require 'pp'
 namespace :redmine do
   desc 'Trac migration script'
   task :migrate_from_trac => :environment do
+    # TODO: Remove this unsupported Trac migration task in a later version.
+    abort "This task is no longer maintained and cannot be used. It will be removed in a future version of Redmine."
 
     module TracMigrate
         TICKET_MAP = []