diff --git a/contracts/cw1155-base/src/contract.rs b/contracts/cw1155-base/src/contract.rs
index a441ac577..5efc844cc 100644
--- a/contracts/cw1155-base/src/contract.rs
+++ b/contracts/cw1155-base/src/contract.rs
@@ -1,6 +1,6 @@
 use cosmwasm_std::{
-    to_binary, Api, Binary, Deps, DepsMut, Env, HumanAddr, MessageInfo, Order, Response, StdResult,
-    Uint128, KV,
+    to_binary, Api, Binary, Deps, DepsMut, Env, HumanAddr, MessageInfo, Order, Response, StdError,
+    StdResult, Uint128, KV,
 };
 use cw_storage_plus::Bound;
 
@@ -83,6 +83,13 @@ pub fn execute(
     }
 }
 
+fn checked_add(a: Uint128, b: Uint128) -> StdResult<Uint128> {
+    a.u128()
+        .checked_add(b.u128())
+        .map(Uint128)
+        .ok_or_else(|| StdError::underflow(a, b)) // FIXME add Overflow error branch in StdError
+}
+
 /// When from is None: mint new coins
 /// When to is None: burn coins
 /// When both are None: not token balance is changed, meaningless but valid
@@ -107,7 +114,9 @@ fn execute_transfer_inner<'a>(
         BALANCES.update(
             deps.storage,
             (canonical_to.as_slice(), token_id),
-            |balance: Option<Uint128>| -> StdResult<_> { Ok(balance.unwrap_or_default() + amount) },
+            |balance: Option<Uint128>| -> StdResult<_> {
+                checked_add(balance.unwrap_or_default(), amount)
+            },
         )?;
     }
 
@@ -1178,6 +1187,83 @@ mod tests {
 
     #[test]
     fn balance_overflow() {
-        // TODO
+        let mut deps = mock_dependencies(&[]);
+        let token1 = "token1".to_owned();
+        let minter: HumanAddr = "minter".into();
+        let user1: HumanAddr = "user1".into();
+        let user2: HumanAddr = "user2".into();
+
+        let env = {
+            let mut env = mock_env();
+            env.block.height = 1;
+            env
+        };
+
+        let msg = InitMsg {
+            minter: minter.clone(),
+        };
+        let res = instantiate(deps.as_mut(), env.clone(), mock_info("operator", &[]), msg).unwrap();
+        assert_eq!(0, res.messages.len());
+
+        execute(
+            deps.as_mut(),
+            env.clone(),
+            mock_info(minter.clone(), &[]),
+            Cw1155HandleMsg::Mint {
+                to: user1.clone(),
+                token_id: token1.clone(),
+                value: u128::MAX.into(),
+                msg: None,
+            },
+        )
+        .unwrap();
+
+        // overflow
+        assert!(matches!(
+            execute(
+                deps.as_mut(),
+                env.clone(),
+                mock_info(minter.clone(), &[]),
+                Cw1155HandleMsg::Mint {
+                    to: user1.clone(),
+                    token_id: token1.clone(),
+                    value: 1u64.into(),
+                    msg: None,
+                },
+            ),
+            Err(_)
+        ));
+
+        assert!(matches!(
+            execute(
+                deps.as_mut(),
+                env.clone(),
+                mock_info(minter.clone(), &[]),
+                Cw1155HandleMsg::Mint {
+                    to: user2.clone(),
+                    token_id: token1.clone(),
+                    value: 1u64.into(),
+                    msg: None,
+                },
+            ),
+            Ok(_)
+        ));
+
+        // overflow
+        assert!(matches!(
+            execute(
+                deps.as_mut(),
+                env.clone(),
+                mock_info(user2.clone(), &[]),
+                Cw1155HandleMsg::SendFrom {
+                    from: user2.clone(),
+                    to: user1.clone(),
+                    token_id: token1.clone(),
+                    value: 1u64.into(),
+                    msg: None,
+                },
+            ),
+            Err(_)
+        ));
     }
 }