diff --git a/contract/contracts/event_registry/src/error.rs b/contract/contracts/event_registry/src/error.rs
index 2e455d2..c472b5c 100644
--- a/contract/contracts/event_registry/src/error.rs
+++ b/contract/contracts/event_registry/src/error.rs
@@ -72,6 +72,8 @@ pub enum EventRegistryError {
     InvalidTargetDeadline = 44,
     /// Admin has already approved this proposal
     AlreadyApproved = 45,
+    /// Two or more ticket tiers share the same ID
+    DuplicateTierId = 46,
 }
 
 impl core::fmt::Display for EventRegistryError {
@@ -216,6 +218,9 @@ impl core::fmt::Display for EventRegistryError {
             EventRegistryError::AlreadyApproved => {
                 write!(f, "Admin has already approved this proposal")
             }
+            EventRegistryError::DuplicateTierId => {
+                write!(f, "Duplicate tier ID: all tier IDs must be unique")
+            }
         }
     }
 }
diff --git a/contract/contracts/event_registry/src/test.rs b/contract/contracts/event_registry/src/test.rs
index 5fd0765..47cf02e 100644
--- a/contract/contracts/event_registry/src/test.rs
+++ b/contract/contracts/event_registry/src/test.rs
@@ -51,6 +51,7 @@ fn test_register_and_get_series() {
         max_supply: 100,
         milestone_plan: None,
         tiers: tiers.clone(),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -68,6 +69,7 @@ fn test_register_and_get_series() {
         max_supply: 100,
         milestone_plan: None,
         tiers: tiers.clone(),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -120,6 +122,7 @@ fn test_issue_and_use_series_pass() {
         max_supply: 100,
         milestone_plan: None,
         tiers: tiers.clone(),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -292,6 +295,7 @@ fn test_storage_operations() {
         current_supply: 0,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -380,6 +384,7 @@ fn test_get_total_tickets_sold_uses_event_current_supply() {
         current_supply: 9,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -483,6 +488,7 @@ fn test_organizer_events_list() {
         current_supply: 0,
         milestone_plan: None,
         tiers: tiers.clone(),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -513,6 +519,7 @@ fn test_organizer_events_list() {
         current_supply: 0,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -672,6 +679,7 @@ fn test_register_event_success() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -789,6 +797,7 @@ fn test_register_event_invalid_target_deadline() {
         max_supply: 100,
         milestone_plan: None,
         tiers: tiers.clone(),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -809,6 +818,7 @@ fn test_register_event_invalid_target_deadline() {
         max_supply: 100,
         milestone_plan: None,
         tiers: tiers.clone(),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -829,6 +839,7 @@ fn test_register_event_invalid_target_deadline() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -865,6 +876,7 @@ fn test_register_event_rejects_contract_as_organizer() {
         max_supply: 100,
         milestone_plan: None,
         tiers: Map::new(&env),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -905,6 +917,7 @@ fn test_register_event_rejects_zero_organizer_address() {
         max_supply: 100,
         milestone_plan: None,
         tiers: Map::new(&env),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -947,6 +960,7 @@ fn test_register_event_unlimited_supply() {
         max_supply: 0,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -991,6 +1005,7 @@ fn test_register_duplicate_event_fails() {
         max_supply: 100,
         milestone_plan: None,
         tiers: tiers.clone(),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1009,6 +1024,7 @@ fn test_register_duplicate_event_fails() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1020,6 +1036,66 @@ fn test_register_duplicate_event_fails() {
     assert_eq!(result, Err(Ok(EventRegistryError::EventAlreadyExists)));
 }
 
+#[test]
+fn test_register_event_duplicate_tier_id_fails() {
+    let env = Env::default();
+    let contract_id = env.register(EventRegistry, ());
+    let client = EventRegistryClient::new(&env, &contract_id);
+
+    let admin = Address::generate(&env);
+    let organizer = Address::generate(&env);
+    let platform_wallet = Address::generate(&env);
+    let usdc_token = Address::generate(&env);
+    env.mock_all_auths();
+    client.initialize(&admin, &platform_wallet, &500, &usdc_token);
+
+    let metadata_cid = String::from_str(
+        &env,
+        "bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi",
+    );
+
+    // Build a map with a duplicate tier ID — Soroban's Map silently keeps the
+    // last value, so the map ends up with one entry instead of two.
+    let tier = TicketTier {
+        name: String::from_str(&env, "General"),
+        price: 1_000,
+        tier_limit: 50,
+        current_sold: 0,
+        is_refundable: true,
+        auction_config: soroban_sdk::vec![&env],
+    };
+    let mut tiers = Map::new(&env);
+    tiers.set(String::from_str(&env, "general"), tier.clone());
+    // Setting the same key again — this is the duplicate
+    tiers.set(String::from_str(&env, "general"), tier);
+
+    let result = client.try_register_event(&EventRegistrationArgs {
+        event_id: String::from_str(&env, "event_dup_tier"),
+        name: String::from_str(&env, "Dup Tier Event"),
+        organizer_address: organizer,
+        payment_address: Address::generate(&env),
+        metadata_cid,
+        max_supply: 0,
+        milestone_plan: None,
+        tiers,
+        // Declare two IDs but the map only has one (duplicate was collapsed)
+        tier_ids: soroban_sdk::vec![
+            &env,
+            String::from_str(&env, "general"),
+            String::from_str(&env, "general"),
+        ],
+        refund_deadline: 0,
+        restocking_fee: 0,
+        resale_cap_bps: None,
+        min_sales_target: None,
+        target_deadline: None,
+        banner_cid: None,
+        tags: None,
+    });
+
+    assert_eq!(result, Err(Ok(EventRegistryError::DuplicateTierId)));
+}
+
 #[test]
 fn test_register_event_invalid_metadata_cid_formats() {
     let env = Env::default();
@@ -1046,6 +1122,7 @@ fn test_register_event_invalid_metadata_cid_formats() {
         max_supply: 100,
         milestone_plan: None,
         tiers: tiers.clone(),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1072,6 +1149,7 @@ fn test_register_event_invalid_metadata_cid_formats() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1098,6 +1176,7 @@ fn test_register_event_invalid_metadata_cid_formats() {
         max_supply: 100,
         milestone_plan: None,
         tiers: Map::new(&env),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1142,6 +1221,7 @@ fn test_get_event_payment_info() {
         max_supply: 50,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1186,6 +1266,7 @@ fn test_update_event_status() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1229,6 +1310,7 @@ fn test_event_inactive_error() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1273,6 +1355,7 @@ fn test_complete_event_lifecycle() {
         max_supply: 200,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1329,6 +1412,7 @@ fn test_update_metadata_success() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1378,6 +1462,7 @@ fn test_update_metadata_invalid_cid() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1473,6 +1558,7 @@ fn test_set_custom_event_fee() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1529,6 +1615,7 @@ fn test_set_custom_event_fee_exceeds_max() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1599,6 +1686,7 @@ fn test_increment_inventory_success() {
         max_supply: 10,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1671,6 +1759,7 @@ fn test_increment_inventory_max_supply_exceeded() {
         max_supply: 2,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1738,6 +1827,7 @@ fn test_increment_inventory_bulk_exceeds_max_supply() {
         max_supply: 3,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1805,6 +1895,7 @@ fn test_increment_inventory_unlimited_supply() {
         max_supply: 0,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1890,6 +1981,7 @@ fn test_increment_inventory_inactive_event() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -1950,6 +2042,7 @@ fn test_increment_inventory_persists_across_reads() {
         max_supply: 50,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2027,6 +2120,7 @@ fn test_tier_limit_exceeds_max_supply() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2087,6 +2181,7 @@ fn test_tier_not_found() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2148,6 +2243,7 @@ fn test_tier_supply_exceeded() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2225,6 +2321,7 @@ fn test_multiple_tiers_inventory() {
         max_supply: 70,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2299,6 +2396,7 @@ fn test_increment_inventory_supply_overflow() {
         current_supply: i128::MAX,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2366,6 +2464,7 @@ fn test_increment_inventory_tier_sold_overflow() {
         current_supply: 0,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2415,6 +2514,7 @@ fn test_update_event_status_noop_skips_event() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2492,6 +2592,7 @@ fn test_blacklist_prevents_event_registration() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2537,6 +2638,7 @@ fn test_update_metadata_noop_skips_event() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2621,6 +2723,7 @@ fn test_blacklist_suspends_active_events() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2747,6 +2850,7 @@ fn test_register_event_with_resale_cap() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: Some(1000), // 10% above face value
@@ -2791,6 +2895,7 @@ fn test_register_event_resale_cap_zero() {
         max_supply: 50,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: Some(0), // No markup allowed
@@ -2835,6 +2940,7 @@ fn test_register_event_resale_cap_none() {
         max_supply: 50,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None, // No cap
@@ -2879,6 +2985,7 @@ fn test_postpone_event_sets_grace_period() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -2930,6 +3037,7 @@ fn test_register_event_resale_cap_invalid() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: Some(10001), // Over 100% - invalid
@@ -2970,6 +3078,7 @@ fn test_cancel_event_success() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 100,
         resale_cap_bps: None,
@@ -3013,6 +3122,7 @@ fn test_archive_event_rejects_active_event() {
         max_supply: 100,
         milestone_plan: None,
         tiers: Map::new(&env),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -3054,6 +3164,7 @@ fn test_cancel_already_cancelled_fails() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -3096,6 +3207,7 @@ fn test_update_status_on_cancelled_event_fails() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -3740,6 +3852,7 @@ fn test_register_event_with_banner_cid() {
         max_supply: 100,
         milestone_plan: None,
         tiers: Map::new(&env),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -3790,6 +3903,7 @@ fn test_goal_met_event_fires_only_once() {
         max_supply: 100,
         milestone_plan: None,
         tiers: soroban_sdk::Map::new(&env),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -3847,6 +3961,7 @@ fn test_register_event_without_banner_cid() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -3914,6 +4029,7 @@ fn test_series_pass_issued_at_timestamp() {
         max_supply: 50,
         milestone_plan: None,
         tiers: soroban_sdk::Map::new(&env),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -3991,6 +4107,7 @@ fn base_args(
         max_supply: 100,
         milestone_plan,
         tiers: Map::new(env),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -4328,6 +4445,7 @@ fn test_cancelled_status_guard() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -4461,6 +4579,7 @@ fn test_register_event_restocking_fee_exceeds_tier_price_fails() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 6_000_000,
         resale_cap_bps: None,
@@ -4516,6 +4635,7 @@ fn test_register_event_restocking_fee_equal_to_tier_price_succeeds() {
         max_supply: 100,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 5_000_000,
         resale_cap_bps: None,
@@ -4567,6 +4687,7 @@ fn test_register_event_restocking_fee_zero_always_valid() {
         max_supply: 50,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
@@ -4845,6 +4966,7 @@ fn tags_base_args(env: &Env, event_id: &str, organizer: &Address) -> EventRegist
         max_supply: 0,
         milestone_plan: None,
         tiers: Map::new(env),
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
diff --git a/contract/contracts/event_registry/src/test_e2e.rs b/contract/contracts/event_registry/src/test_e2e.rs
index bfc7b96..290ce11 100644
--- a/contract/contracts/event_registry/src/test_e2e.rs
+++ b/contract/contracts/event_registry/src/test_e2e.rs
@@ -42,6 +42,7 @@ fn make_event_args(
         max_supply,
         milestone_plan: None,
         tiers,
+        tier_ids: soroban_sdk::vec![&env],
         refund_deadline: 0,
         restocking_fee: 0,
         resale_cap_bps: None,
diff --git a/contract/contracts/event_registry/src/types.rs b/contract/contracts/event_registry/src/types.rs
index c76be83..2c598fd 100644
--- a/contract/contracts/event_registry/src/types.rs
+++ b/contract/contracts/event_registry/src/types.rs
@@ -167,7 +167,13 @@ pub struct EventRegistrationArgs {
     pub metadata_cid: String,
     pub max_supply: i128,
     pub milestone_plan: Option<Vec<Milestone>>,
+    /// Map of tier_id to TicketTier for multi-tiered pricing.
     pub tiers: Map<String, TicketTier>,
+    /// Explicit list of all tier IDs being registered. Must have the same
+    /// length as `tiers` — if a duplicate ID was set in `tiers`, the map
+    /// silently collapses it and the lengths will differ, triggering
+    /// `DuplicateTierId`.
+    pub tier_ids: Vec<String>,
     pub refund_deadline: u64,
     pub restocking_fee: i128,
     /// Optional resale price cap in basis points above face value.