diff --git a/cmd/server/tests/sync_integration_test.go b/cmd/server/tests/sync_integration_test.go
index 1350284..9dc5819 100644
--- a/cmd/server/tests/sync_integration_test.go
+++ b/cmd/server/tests/sync_integration_test.go
@@ -37,7 +37,7 @@ func setupSyncTestDB(t *testing.T) *database.Queries {
 		_, _ = dbPool.Exec(ctx, "DELETE FROM media_items WHERE title LIKE 'Test %'")
 		_, _ = dbPool.Exec(ctx, "DELETE FROM libraries WHERE name LIKE 'Test %'")
 		_, _ = dbPool.Exec(ctx, "DELETE FROM devices WHERE device_name LIKE 'Test %'")
-		_, _ = dbPool.Exec(ctx, "DELETE FROM users WHERE email LIKE 'test%'")
+		_, _ = dbPool.Exec(ctx, "DELETE FROM users WHERE email LIKE 'test-sync%'")
 		dbPool.Close()
 	})
 
diff --git a/cmd/server/tests/test_helpers_test.go b/cmd/server/tests/test_helpers_test.go
index 43e00a9..a79906d 100644
--- a/cmd/server/tests/test_helpers_test.go
+++ b/cmd/server/tests/test_helpers_test.go
@@ -558,11 +558,15 @@ func setupTestServer(t *testing.T) *TestServerSetup {
 
 	ctx := context.Background()
 
-	// Delete ALL test users (any user with test email domains) to ensure clean state
-	// This handles users created during tests that may have been promoted to admin, etc.
+	// Delete transient test users but preserve the dev admin user
+	// testuser@tests.bookhoard.internal is the shared dev admin — deleting it
+	// triggers ON DELETE SET NULL on libraries.created_by_admin_id
 	allUsers, err := queries.ListUsers(ctx)
 	if err == nil {
 		for _, user := range allUsers {
+			if user.Email == "testuser@tests.bookhoard.internal" {
+				continue
+			}
 			if strings.HasSuffix(user.Email, "@example.com") || strings.HasSuffix(user.Email, "@tests.bookhoard.internal") {
 				queries.DeleteUser(ctx, user.ID)
 			}