diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2ba7e52f8..483336b04 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Security
   -->
 
+## [3.0.1] - 2024-09-07
+### Fixed
+* #1491 Fix migration error when there are pre-existing Access Tokens.
+
 ## [3.0.0] - 2024-09-05
 
 ### WARNING - POTENTIAL BREAKING CHANGES
diff --git a/oauth2_provider/__init__.py b/oauth2_provider/__init__.py
index 528787cfc..055276878 100644
--- a/oauth2_provider/__init__.py
+++ b/oauth2_provider/__init__.py
@@ -1 +1 @@
-__version__ = "3.0.0"
+__version__ = "3.0.1"
diff --git a/oauth2_provider/migrations/0012_add_token_checksum.py b/oauth2_provider/migrations/0012_add_token_checksum.py
index 7f62955e3..476c3b402 100644
--- a/oauth2_provider/migrations/0012_add_token_checksum.py
+++ b/oauth2_provider/migrations/0012_add_token_checksum.py
@@ -4,6 +4,16 @@
 from django.db import migrations, models
 from oauth2_provider.settings import oauth2_settings
 
+def forwards_func(apps, schema_editor):
+    """
+    Forward migration touches every "old" accesstoken.token which will cause the checksum to be computed.
+    """
+    AccessToken = apps.get_model(oauth2_settings.ACCESS_TOKEN_MODEL)
+    accesstokens = AccessToken._default_manager.all()
+    for accesstoken in accesstokens:
+        accesstoken.save(update_fields=['token_checksum'])
+
+
 class Migration(migrations.Migration):
     dependencies = [
         ("oauth2_provider", "0011_refreshtoken_token_family"),
@@ -14,13 +24,17 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name="accesstoken",
             name="token_checksum",
-            field=oauth2_provider.models.TokenChecksumField(
-                blank=True, db_index=True, max_length=64, unique=True
-            ),
+            field=oauth2_provider.models.TokenChecksumField(blank=True, null=True, max_length=64),
         ),
         migrations.AlterField(
             model_name="accesstoken",
             name="token",
             field=models.TextField(),
         ),
+        migrations.RunPython(forwards_func, migrations.RunPython.noop),
+        migrations.AlterField(
+            model_name='accesstoken',
+            name='token_checksum',
+            field=oauth2_provider.models.TokenChecksumField(blank=False, max_length=64,  db_index=True, unique=True),
+        ),
     ]
diff --git a/oauth2_provider/models.py b/oauth2_provider/models.py
index 831fc551f..a987b4435 100644
--- a/oauth2_provider/models.py
+++ b/oauth2_provider/models.py
@@ -392,7 +392,7 @@ class AbstractAccessToken(models.Model):
     token = models.TextField()
     token_checksum = TokenChecksumField(
         max_length=64,
-        blank=True,
+        blank=False,
         unique=True,
         db_index=True,
     )