diff --git a/app/activitypub/util.py b/app/activitypub/util.py
index f0811f7a..5c1807a2 100644
--- a/app/activitypub/util.py
+++ b/app/activitypub/util.py
@@ -1208,7 +1208,7 @@ def find_reported_object(ap_id) -> Union[User, Post, PostReply, None]:
 
 
 def find_instance_id(server):
-    server = server.strip()
+    server = server.strip().lower()
     instance = Instance.query.filter_by(domain=server).first()
     if instance:
         return instance.id
@@ -1216,8 +1216,11 @@ def find_instance_id(server):
         # Our instance does not know about {server} yet. Initially, create a sparse row in the 'instance' table and spawn a background
         # task to update the row with more details later
         new_instance = Instance(domain=server, software='unknown', created_at=utcnow(), trusted=server == 'piefed.social')
-        db.session.add(new_instance)
-        db.session.commit()
+        try:
+            db.session.add(new_instance)
+            db.session.commit()
+        except IntegrityError:
+            return Instance.query.filter_by(domain=server).one()
 
         # Spawn background task to fill in more details
         new_instance_profile(new_instance.id)
diff --git a/app/models.py b/app/models.py
index 96bec31c..caf7a414 100644
--- a/app/models.py
+++ b/app/models.py
@@ -52,7 +52,7 @@ class AllowedInstances(db.Model):
 
 class Instance(db.Model):
     id = db.Column(db.Integer, primary_key=True)
-    domain = db.Column(db.String(256), index=True)
+    domain = db.Column(db.String(256), index=True, unique=True)
     inbox = db.Column(db.String(256))
     shared_inbox = db.Column(db.String(256))
     outbox = db.Column(db.String(256))
diff --git a/migrations/versions/d88b49617de0_unique_instance_domain.py b/migrations/versions/d88b49617de0_unique_instance_domain.py
new file mode 100644
index 00000000..a4d65bec
--- /dev/null
+++ b/migrations/versions/d88b49617de0_unique_instance_domain.py
@@ -0,0 +1,74 @@
+"""unique instance domain
+
+Revision ID: d88b49617de0
+Revises: c3cc707ab5e9
+Create Date: 2024-11-24 16:22:16.733285
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy import text
+
+# revision identifiers, used by Alembic.
+revision = 'd88b49617de0'
+down_revision = 'c3cc707ab5e9'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # Find duplicate communities by ap_profile_id
+    dupes_query = text('''
+                SELECT domain FROM "instance" 
+                GROUP BY domain 
+                HAVING COUNT(*) > 1
+            ''')
+
+    conn = op.get_bind()
+    duplicate_instances = conn.execute(dupes_query).scalars()
+    print('Cleaning up duplicate instances...')
+
+    for domain in duplicate_instances:
+        if domain is None:
+            continue
+        # Get all communities with the same ap_profile_id, ordered by ID
+        users_query = text('''
+                    SELECT id FROM "instance" 
+                    WHERE domain = :domain 
+                    ORDER BY id
+                ''')
+        instances = conn.execute(users_query, {"domain": domain}).fetchall()
+
+        # Set the lowest ID as the new_id, and collect other IDs to update/delete
+        new_id = instances[0].id
+        old_ids = [instance.id for instance in instances[1:]]
+
+        print(domain)
+
+        if old_ids:
+            # Update tables with batch IN clause
+            conn.execute(text('UPDATE "community" SET instance_id = :new_id WHERE instance_id IN :old_ids'), {"new_id": new_id, "old_ids": tuple(old_ids)})
+            conn.execute(text('UPDATE "user" SET instance_id = :new_id WHERE instance_id IN :old_ids'), {"new_id": new_id, "old_ids": tuple(old_ids)})
+            conn.execute(text('UPDATE "post" SET instance_id = :new_id WHERE instance_id IN :old_ids'), {"new_id": new_id, "old_ids": tuple(old_ids)})
+            conn.execute(text('UPDATE "post_reply" SET instance_id = :new_id WHERE instance_id IN :old_ids'), {"new_id": new_id, "old_ids": tuple(old_ids)})
+            conn.execute(text('UPDATE "report" SET source_instance_id = :new_id WHERE source_instance_id IN :old_ids'), {"new_id": new_id, "old_ids": tuple(old_ids)})
+            conn.execute(text('DELETE FROM "instance_role" WHERE instance_id IN :old_ids'), {"old_ids": tuple(old_ids)})
+            conn.execute(text('DELETE FROM "instance_block" WHERE instance_id IN :old_ids'), {"old_ids": tuple(old_ids)})
+
+            # Delete the duplicate instances
+            conn.execute(text('DELETE FROM "instance" WHERE id IN :old_ids'), {"old_ids": tuple(old_ids)})
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('instance', schema=None) as batch_op:
+        batch_op.drop_index('ix_instance_domain')
+        batch_op.create_index(batch_op.f('ix_instance_domain'), ['domain'], unique=True)
+
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    with op.batch_alter_table('instance', schema=None) as batch_op:
+        batch_op.drop_index(batch_op.f('ix_instance_domain'))
+        batch_op.create_index('ix_instance_domain', ['domain'], unique=False)
+
+    # ### end Alembic commands ###