diff --git a/INVARIANTS.md b/INVARIANTS.md
index f1277cbb..b4ccd10c 100644
--- a/INVARIANTS.md
+++ b/INVARIANTS.md
@@ -1,12 +1,12 @@
 ## Vault Balance Invariant
 
-**Invariant**: For every reachable state of the `CalloraVault` contract, the stored balance in `VaultMeta.balance` is always **greater than or equal to 0**.
+**Invariant**: For every reachable state of the `CalloraVault` contract, the stored balance in `VaultMeta.balance` is always **greater than or equal to 0** and **less than or equal to i128::MAX**.
 
 - **Storage field**: `VaultMeta.balance : i128`
 - **Accessors**:
   - `get_meta(env: Env) -> VaultMeta`
   - `balance(env: Env) -> i128`
-- **Guarantee**: Any value returned by `get_meta(env).balance` or `balance(env)` is **never negative**.
+- **Guarantee**: Any value returned by `get_meta(env).balance` or `balance(env)` is **never negative** and **cannot overflow** the `i128` numeric boundary. Any operation that would cause an overflow (e.g., `deposit` past `i128::MAX`) will panic and revert the transaction.
 
 This document lists all functions that can change the stored balance and the pre-/post-conditions that preserve this invariant.
 
diff --git a/contracts/vault/src/test.rs b/contracts/vault/src/test.rs
index 72c5c391..92a8170b 100644
--- a/contracts/vault/src/test.rs
+++ b/contracts/vault/src/test.rs
@@ -1997,6 +1997,36 @@ fn get_revenue_pool_consistency_with_zero_balance() {
     assert_eq!(client.get_revenue_pool(), Some(pool));
 }
 
+#[test]
+fn deposit_max_balance_overflow_panic() {
+    // Explicit test for max-balance overflow near i128::MAX.
+    // Exercises the checked_add(...).unwrap_or_else(|| panic!("balance overflow")) path.
+    let env = Env::default();
+    let owner = Address::generate(&env);
+    let (vault_address, client) = create_vault(&env);
+    let (usdc, usdc_client, usdc_admin) = create_usdc(&env, &owner);
+
+    env.mock_all_auths();
+
+    // 1. Setup vault balance near i128::MAX
+    let near_max = i128::MAX - 1;
+    let overflow_amount = 2;
+
+    fund_vault(&usdc_admin, &vault_address, near_max);
+    client.init(&owner, &usdc, &Some(near_max), &None, &None, &None, &None);
+
+    // 2. Prepare overflow deposit
+    usdc_admin.mint(&owner, &overflow_amount);
+    usdc_client.approve(&owner, &vault_address, &overflow_amount, &1000);
+
+    // 3. Confirm it panics safely on overflow
+    let result = client.try_deposit(&owner, &overflow_amount);
+    assert!(
+        result.is_err(),
+        "contract must fail safely when balance would overflow i128::MAX"
+    );
+}
+
 #[test]
 fn get_revenue_pool_after_multiple_sequential_updates() {
     // Test multiple sequential set/clear operations before query