diff --git a/changelog/7778.md b/changelog/7778.md
index 2f1c2f9042..0926dd3b8b 100644
--- a/changelog/7778.md
+++ b/changelog/7778.md
@@ -1,5 +1,9 @@
 ### Added
 
-- settings: move A4_PROJECT_TOPICS to Enum class 
+- settings: move A4_PROJECT_TOPICS to Enum class
 - apps/plans: topics as an m2m relation to plans, replacing django-multiselectfield
 - apps/projects: topics from TopicEnum, topic form and serializer for projects
+- **Breaking Change** Plan topics with a code longer than 3 chars will be dropped.
+  If you need to keep them modify the check in
+  `meinberlin/apps/plans/migratiosn/0059_migrate_topics_to_m2m_topics.py` or
+  migrate them to shorter codes. Note: the max. possible length is still limited to 10.
diff --git a/meinberlin/apps/plans/migrations/0059_migrate_topics_to_m2m_topics.py b/meinberlin/apps/plans/migrations/0059_migrate_topics_to_m2m_topics.py
index 8057a56c1d..b2b40d34f9 100644
--- a/meinberlin/apps/plans/migrations/0059_migrate_topics_to_m2m_topics.py
+++ b/meinberlin/apps/plans/migrations/0059_migrate_topics_to_m2m_topics.py
@@ -1,19 +1,36 @@
 # Generated by Django 4.2 on 2023-11-29 13:20
+import logging
 
 from django.db import migrations
 from django.conf import settings
 
+logger = logging.getLogger(__name__)
+
 
 def add_topics_to_m2m_table(apps, schema_editor):
     if hasattr(settings, "A4_PROJECT_TOPICS"):
         plans = apps.get_model("meinberlin_plans", "Plan")
         topic = apps.get_model("a4projects", "Topic")
         for plan in plans.objects.all():
-            for topic_code in plan.topics:
-                plan_topic, _ = topic.objects.get_or_create(
-                    code=topic_code,
+            try:
+                for topic_code in plan.topics.split(","):
+                    if not topic_code:
+                        continue
+                    if len(topic_code) > 3:
+                        logger.warning(
+                            "warning: dropping unknown topic:"
+                            + topic_code
+                            + ". Max length is 3"
+                        )
+                        continue
+                    plan_topic, _ = topic.objects.get_or_create(
+                        code=topic_code,
+                    )
+                    plan.m2mtopics.add(plan_topic)
+            except Exception as e:
+                logger.warning(
+                    "error migrating topics for plan " + plan.title + ": " + str(e)
                 )
-                plan.m2mtopics.add(plan_topic)
     else:
         pass