diff --git a/issues/migrations/0014_alter_grouping_unique_together.py b/issues/migrations/0014_alter_grouping_unique_together.py
new file mode 100644
index 0000000..9ffcbbe
--- /dev/null
+++ b/issues/migrations/0014_alter_grouping_unique_together.py
@@ -0,0 +1,16 @@
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("projects", "0011_fill_stored_event_count"),
+        ("issues", "0013_fix_issue_stored_event_counts"),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name="grouping",
+            unique_together={("project", "grouping_key")},
+        ),
+    ]
diff --git a/issues/models.py b/issues/models.py
index 69a320c..ac8daba 100644
--- a/issues/models.py
+++ b/issues/models.py
@@ -198,8 +198,8 @@ class Grouping(models.Model):
         "projects.Project", blank=False, null=True, on_delete=models.SET_NULL)  # SET_NULL: cleanup 'later'
 
     # NOTE: I don't want to have any principled maximum on the grouping key, nor do I want to prematurely optimize the
-    # lookup. If lookups are slow, we _could_ examine whether manually hashing these values and matching on the hash
-    # helps.
+    # lookup. If lookups are slow (even with an index), we _could_ examine whether manually hashing these values and
+    # matching on the hash helps.
     grouping_key = models.TextField(blank=False, null=False)
 
     issue = models.ForeignKey("Issue", blank=False, null=True, on_delete=models.SET_NULL)  # SET_NULL: cleanup 'later'
@@ -207,6 +207,13 @@ class Grouping(models.Model):
     def __str__(self):
         return self.grouping_key
 
+    class Meta:
+        unique_together = [
+            # principled: grouping _key_ is a _key_ for a reason (within a project). This also implies the main way of
+            # looking up groupings has an appropriate index.
+            ("project", "grouping_key"),
+        ]
+
 
 def format_unmute_reason(unmute_metadata):
     if "mute_until" in unmute_metadata: