diff --git a/lms/migrations/versions/7858a12c4e4a_add_index_for_user_deduplication.py b/lms/migrations/versions/7858a12c4e4a_add_index_for_user_deduplication.py
new file mode 100644
index 0000000000..e216b01e41
--- /dev/null
+++ b/lms/migrations/versions/7858a12c4e4a_add_index_for_user_deduplication.py
@@ -0,0 +1,24 @@
+"""Add index for user deduplication."""
+
+import sqlalchemy as sa
+from alembic import op
+
+revision = "7858a12c4e4a"
+down_revision = "f6c442c861c4"
+
+
+def upgrade() -> None:
+    # CONCURRENTLY can't be used inside a transaction. Finish the current one.
+    op.execute("COMMIT")
+
+    op.create_index(
+        "ix__user_h_user_updated",
+        "user",
+        ["h_userid", sa.text("updated DESC")],
+        unique=False,
+        postgresql_concurrently=True,
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix__user_h_user_updated", table_name="user")
diff --git a/lms/models/user.py b/lms/models/user.py
index b1d9bc399c..9c688a84a7 100644
--- a/lms/models/user.py
+++ b/lms/models/user.py
@@ -20,6 +20,7 @@ class User(CreatedUpdatedMixin, Base):
             "h_userid",
             name="uq__user__application_instance_id__h_userid",
         ),
+        sa.Index("ix__user_h_user_updated", "h_userid", sa.desc("updated")),
     )
 
     id = sa.Column(sa.Integer, autoincrement=True, primary_key=True)