diff --git a/backend/windmill-api-integration-tests/tests/datatable_roles.rs b/backend/windmill-api-integration-tests/tests/datatable_roles.rs
index d8a44d7a55..e3269c8138 100644
--- a/backend/windmill-api-integration-tests/tests/datatable_roles.rs
+++ b/backend/windmill-api-integration-tests/tests/datatable_roles.rs
@@ -934,3 +934,39 @@ async fn a_settings_save_dropping_a_governing_entry_names_the_forks_it_strands(
     );
     Ok(())
 }
+
+#[sqlx::test(migrations = "../migrations", fixtures("base", "datatable_roles"))]
+async fn a_save_replacing_an_entry_under_roles_on_its_database_is_refused(
+    db: Pool<Postgres>,
+) -> anyhow::Result<()> {
+    initialize_tracing().await;
+    let server = ApiServer::start(db.clone()).await?;
+    // A rename as a settings sync sends it: the whole map, no `renames`.
+    let resp = authed(
+        client().post(format!(
+            "http://localhost:{}/api/w/test-workspace/workspaces/edit_datatable_config",
+            server.addr.port()
+        )),
+        "SECRET_TOKEN",
+    )
+    .json(&json!({ "settings": { "datatables": {
+        "main_renamed": { "database": { "resource_type": "instance", "resource_path": "dt_main" } }
+    } } }))
+    .send()
+    .await?;
+    let status = resp.status();
+    let body = resp.text().await?;
+    assert_eq!(
+        status, 400,
+        "a save dropped the roles of the database it kept: {body}"
+    );
+
+    let still_governed: bool = sqlx::query_scalar(
+        "SELECT (datatable->'datatables'->'main') ? 'permissions' FROM workspace_settings
+         WHERE workspace_id = 'test-workspace'",
+    )
+    .fetch_one(&db)
+    .await?;
+    assert!(still_governed, "the refused save still took effect");
+    Ok(())
+}
diff --git a/backend/windmill-api-workspaces/src/workspaces.rs b/backend/windmill-api-workspaces/src/workspaces.rs
index cfd3c47593..1e591e742e 100644
--- a/backend/windmill-api-workspaces/src/workspaces.rs
+++ b/backend/windmill-api-workspaces/src/workspaces.rs
@@ -3883,6 +3883,40 @@ async fn edit_datatable_config(
         .cloned()
         .collect();
 
+    // Roles follow an entry only through a declared rename. A save that drops an entry under roles
+    // and adds another on the same database without one — which is how a settings sync sends a
+    // rename — would leave that database answering everyone as `admin`.
+    for name in &removed {
+        let Some(old_db) = old_datatables
+            .get(name)
+            .filter(|old| old.permissions.is_some())
+            .and_then(|old| old.database.as_ref())
+        else {
+            continue;
+        };
+        let added_on_same_database =
+            new_config
+                .settings
+                .datatables
+                .iter()
+                .find_map(|(added, dt)| {
+                    let db = dt.database.as_ref()?;
+                    (!old_datatables.contains_key(added)
+                        && !new_config.renames.iter().any(|r| &r.to == added)
+                        && db.resource_type == old_db.resource_type
+                        && db.resource_path == old_db.resource_path)
+                        .then_some(added)
+                });
+        if let Some(added) = added_on_same_database {
+            return Err(Error::BadRequest(format!(
+                "Data table '{name}' is under roles, and this save removes it while adding '{added}' \
+                 on the same database. Its roles would not carry over, leaving that database open to \
+                 everyone as `admin`. Rename it from the data table settings, which carries its \
+                 roles, or turn its roles off first."
+            )));
+        }
+    }
+
     let config: serde_json::Value = serde_json::to_value(new_config.settings)
         .map_err(|err| Error::internal_err(err.to_string()))?;