diff --git a/crates/api/src/admin_objects.rs b/crates/api/src/admin_objects.rs
index 8d3229b..1b2d1b6 100644
--- a/crates/api/src/admin_objects.rs
+++ b/crates/api/src/admin_objects.rs
@@ -500,6 +500,8 @@ pub(crate) async fn create_field_definition(
                 Some("23505") => Err(StatusCode::CONFLICT),
                 // Referenced vocabulary doesn't exist — client error, not server fault.
                 Some("23503") => Err(StatusCode::UNPROCESSABLE_ENTITY),
+                // CHECK constraint violated (e.g. empty key) — client error.
+                Some("23514") => Err(StatusCode::UNPROCESSABLE_ENTITY),
                 _ => Err(StatusCode::INTERNAL_SERVER_ERROR),
             }
         }
diff --git a/crates/api/tests/admin_fields.rs b/crates/api/tests/admin_fields.rs
index a6a9fe0..f4408d3 100644
--- a/crates/api/tests/admin_fields.rs
+++ b/crates/api/tests/admin_fields.rs
@@ -284,3 +284,24 @@ async fn create_authority_field(pool: PgPool) {
 
     assert_eq!(resp.status(), StatusCode::CREATED);
 }
+
+#[sqlx::test(migrations = "../db/migrations")]
+async fn empty_key_is_422(pool: PgPool) {
+    migrate_sessions(&db::Db::from_pool(pool.clone()))
+        .await
+        .unwrap();
+
+    seed_user(&pool, "ed@example.com", "pw-editor-123", Role::Editor).await;
+
+    let app = build_app(state(pool));
+    let cookie = login(&app, "ed@example.com", "pw-editor-123").await;
+
+    let resp = post_field(
+        &app,
+        &cookie,
+        r#"{"key":"","data_type":"text","required":false,"labels":[{"lang":"en","label":"X"}]}"#,
+    )
+    .await;
+
+    assert_eq!(resp.status(), StatusCode::UNPROCESSABLE_ENTITY);
+}