diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index bd7b0897..39df10cb 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -15,6 +15,8 @@ Unreleased
 **********
 
 * Add support for Typesense as the search backend.
+* Fix: Set default value for ``pinned`` field on ``CommentThread`` to ``False``
+  to prevent NULL sort bug.
 
 0.3.4 – 2025-08-13
 ******************
diff --git a/forum/__init__.py b/forum/__init__.py
index bc1fa6c4..255a215f 100644
--- a/forum/__init__.py
+++ b/forum/__init__.py
@@ -2,4 +2,4 @@
 Openedx forum app.
 """
 
-__version__ = "0.4.0"
+__version__ = "0.4.1"
diff --git a/forum/backends/mysql/api.py b/forum/backends/mysql/api.py
index b115119b..c383d31a 100644
--- a/forum/backends/mysql/api.py
+++ b/forum/backends/mysql/api.py
@@ -1865,6 +1865,7 @@ def create_thread(data: dict[str, Any]) -> str:
             thread_type=data.get("thread_type", "discussion"),
             context=data.get("context", "course"),
             last_activity_at=timezone.now(),
+            pinned=data.get("pinned", False),
             **optional_args,
         )
         return str(new_thread.pk)
diff --git a/forum/backends/mysql/models.py b/forum/backends/mysql/models.py
index 3924a0d6..211d1ff5 100644
--- a/forum/backends/mysql/models.py
+++ b/forum/backends/mysql/models.py
@@ -239,7 +239,7 @@ class CommentThread(Content):
     )
     closed: models.BooleanField[bool, bool] = models.BooleanField(default=False)
     pinned: models.BooleanField[Optional[bool], bool] = models.BooleanField(
-        null=True, blank=True
+        default=False
     )
     last_activity_at: models.DateTimeField[Optional[datetime], datetime] = (
         models.DateTimeField(null=True, blank=True)
diff --git a/forum/migration_helpers.py b/forum/migration_helpers.py
index f47d5672..fb3a79a9 100644
--- a/forum/migration_helpers.py
+++ b/forum/migration_helpers.py
@@ -122,7 +122,7 @@ def create_or_update_thread(thread_data: dict[str, Any]) -> None:
             anonymous=thread_data.get("anonymous", False),
             anonymous_to_peers=thread_data.get("anonymous_to_peers", False),
             closed=thread_data.get("closed", False),
-            pinned=thread_data.get("pinned"),
+            pinned=thread_data.get("pinned", False),
             last_activity_at=make_aware(thread_data["last_activity_at"]),
             commentable_id=thread_data.get("commentable_id"),
         )
diff --git a/forum/migrations/0005_alter_commentthread_pinned.py b/forum/migrations/0005_alter_commentthread_pinned.py
new file mode 100644
index 00000000..c95ebcc6
--- /dev/null
+++ b/forum/migrations/0005_alter_commentthread_pinned.py
@@ -0,0 +1,26 @@
+# Generated by Django 5.2.12 on 2026-03-27 06:58
+
+from typing import Any
+
+from django.db import migrations, models
+
+
+def backfill_pinned_false(apps: Any, schema_editor: Any) -> None:
+    CommentThread = apps.get_model("forum", "CommentThread")
+    CommentThread.objects.filter(pinned__isnull=True).update(pinned=False)
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("forum", "0004_add_author_username_fields"),
+    ]
+
+    operations = [
+        migrations.RunPython(backfill_pinned_false, migrations.RunPython.noop),
+        migrations.AlterField(
+            model_name="commentthread",
+            name="pinned",
+            field=models.BooleanField(default=False),
+        ),
+    ]
diff --git a/tests/test_backends/test_mysql/test_models.py b/tests/test_backends/test_mysql/test_models.py
index f483970e..6598c13a 100644
--- a/tests/test_backends/test_mysql/test_models.py
+++ b/tests/test_backends/test_mysql/test_models.py
@@ -106,7 +106,7 @@ def test_comment_thread_creation() -> None:
     assert comment_thread.thread_type == "discussion"
     assert comment_thread.context == "course"
     assert comment_thread.closed is False
-    assert comment_thread.pinned is None
+    assert comment_thread.pinned is False
 
 
 @pytest.mark.django_db