diff --git a/common/src/asset.rs b/common/src/asset.rs
index e3c72727..9fdbe2bd 100644
--- a/common/src/asset.rs
+++ b/common/src/asset.rs
@@ -506,4 +506,100 @@ mod tests {
         let deserialized: BorrowAssetAmount = serde_json::from_str(&serialized).unwrap();
         assert_eq!(deserialized, amount);
     }
+
+    #[test]
+    fn checked_add() {
+        let v = BorrowAssetAmount::new(0).checked_add(BorrowAssetAmount::new(0));
+        assert_eq!(v, Some(BorrowAssetAmount::new(0)));
+        let v = BorrowAssetAmount::new(0).checked_add(BorrowAssetAmount::new(100));
+        assert_eq!(v, Some(BorrowAssetAmount::new(100)));
+        let v = BorrowAssetAmount::new(100).checked_add(BorrowAssetAmount::new(0));
+        assert_eq!(v, Some(BorrowAssetAmount::new(100)));
+        let v = BorrowAssetAmount::new(100).checked_add(BorrowAssetAmount::new(100));
+        assert_eq!(v, Some(BorrowAssetAmount::new(200)));
+        let v = BorrowAssetAmount::new(1).checked_add(BorrowAssetAmount::new(u128::MAX));
+        assert_eq!(v, None);
+    }
+
+    #[test]
+    fn checked_sub() {
+        let v = BorrowAssetAmount::new(0).checked_sub(BorrowAssetAmount::new(0));
+        assert_eq!(v, Some(BorrowAssetAmount::new(0)));
+        let v = BorrowAssetAmount::new(0).checked_sub(BorrowAssetAmount::new(100));
+        assert_eq!(v, None);
+        let v = BorrowAssetAmount::new(100).checked_sub(BorrowAssetAmount::new(0));
+        assert_eq!(v, Some(BorrowAssetAmount::new(100)));
+        let v = BorrowAssetAmount::new(100).checked_sub(BorrowAssetAmount::new(100));
+        assert_eq!(v, Some(BorrowAssetAmount::new(0)));
+        let v = BorrowAssetAmount::new(1).checked_sub(BorrowAssetAmount::new(u128::MAX - 33));
+        assert_eq!(v, None);
+    }
+
+    #[test]
+    fn saturating_add() {
+        let v = BorrowAssetAmount::new(0).saturating_add(BorrowAssetAmount::new(0));
+        assert_eq!(v, BorrowAssetAmount::new(0));
+        let v = BorrowAssetAmount::new(0).saturating_add(BorrowAssetAmount::new(100));
+        assert_eq!(v, BorrowAssetAmount::new(100));
+        let v = BorrowAssetAmount::new(100).saturating_add(BorrowAssetAmount::new(0));
+        assert_eq!(v, BorrowAssetAmount::new(100));
+        let v = BorrowAssetAmount::new(100).saturating_add(BorrowAssetAmount::new(100));
+        assert_eq!(v, BorrowAssetAmount::new(200));
+        let v = BorrowAssetAmount::new(100).saturating_add(BorrowAssetAmount::new(u128::MAX - 33));
+        assert_eq!(v, BorrowAssetAmount::new(u128::MAX));
+    }
+
+    #[test]
+    fn saturating_sub() {
+        let v = BorrowAssetAmount::new(0).saturating_sub(BorrowAssetAmount::new(0));
+        assert_eq!(v, BorrowAssetAmount::new(0));
+        let v = BorrowAssetAmount::new(0).saturating_sub(BorrowAssetAmount::new(100));
+        assert_eq!(v, BorrowAssetAmount::new(0));
+        let v = BorrowAssetAmount::new(100).saturating_sub(BorrowAssetAmount::new(0));
+        assert_eq!(v, BorrowAssetAmount::new(100));
+        let v = BorrowAssetAmount::new(100).saturating_sub(BorrowAssetAmount::new(100));
+        assert_eq!(v, BorrowAssetAmount::new(0));
+        let v = BorrowAssetAmount::new(100).saturating_sub(BorrowAssetAmount::new(u128::MAX - 33));
+        assert_eq!(v, BorrowAssetAmount::new(0));
+    }
+
+    #[test]
+    #[should_panic = "overflow"]
+    fn overflow_unwrap_add() {
+        let _ =
+            BorrowAssetAmount::new(100).unwrap_add(BorrowAssetAmount::new(u128::MAX), "overflow");
+    }
+
+    #[test]
+    #[should_panic = "overflow"]
+    fn overflow_unwrap_sub() {
+        let _ =
+            BorrowAssetAmount::new(100).unwrap_sub(BorrowAssetAmount::new(u128::MAX), "overflow");
+    }
+
+    #[test]
+    #[should_panic = "attempt to add with overflow"]
+    fn overflow_add() {
+        let _ = BorrowAssetAmount::new(u128::MAX) + BorrowAssetAmount::new(1);
+    }
+
+    #[test]
+    #[should_panic = "attempt to add with overflow"]
+    fn overflow_add_assign() {
+        let mut v = BorrowAssetAmount::new(u128::MAX);
+        v += BorrowAssetAmount::new(1);
+    }
+
+    #[test]
+    #[should_panic = "attempt to subtract with overflow"]
+    fn overflow_sub() {
+        let _ = BorrowAssetAmount::new(0) - BorrowAssetAmount::new(1);
+    }
+
+    #[test]
+    #[should_panic = "attempt to subtract with overflow"]
+    fn overflow_sub_assign() {
+        let mut v = BorrowAssetAmount::new(1);
+        v -= BorrowAssetAmount::new(u128::MAX);
+    }
 }
diff --git a/contract/market/tests/collateral.rs b/contract/market/tests/collateral.rs
index cf22c2dc..ce064e63 100644
--- a/contract/market/tests/collateral.rs
+++ b/contract/market/tests/collateral.rs
@@ -64,3 +64,18 @@ async fn collateral_withdrawal(#[future(awt)] worker: Worker<Sandbox>) {
 
     assert_eq!(withdrawn + collateral_deposit, total);
 }
+
+#[rstest]
+#[tokio::test]
+#[should_panic = "attempt to subtract with overflow"]
+async fn excessive_collateral_withdrawal(#[future(awt)] worker: Worker<Sandbox>) {
+    setup_test!(worker extract(c) accounts(borrow_user_1, borrow_user_2));
+
+    c.collateralize(&borrow_user_1, 1_000_000).await;
+    c.collateralize(&borrow_user_2, 1_000_000).await;
+
+    let balance_before = c.collateral_asset.balance_of(borrow_user_1.id()).await;
+    eprintln!("Balance before: {balance_before}");
+
+    c.withdraw_collateral(&borrow_user_1, 1_000_000 + 1).await;
+}