diff --git a/src/meta-morpho.ts b/src/meta-morpho.ts
index 55b16dc..e7ebc3d 100644
--- a/src/meta-morpho.ts
+++ b/src/meta-morpho.ts
@@ -2,7 +2,8 @@ import { Address, BigInt, Bytes, log } from "@graphprotocol/graph-ts";
 
 import {
   AllocatorSet,
-  FeeRecipient, MetaMorpho,
+  FeeRecipient,
+  MetaMorpho,
   MetaMorphoAllocator,
   MetaMorphoDeposit,
   MetaMorphoMarket,
diff --git a/src/morpho-blue.ts b/src/morpho-blue.ts
index 7c57a16..dfd751a 100644
--- a/src/morpho-blue.ts
+++ b/src/morpho-blue.ts
@@ -33,6 +33,7 @@ import {
 import { DataManager } from "./sdk/manager";
 import { PositionManager } from "./sdk/position";
 import { TokenManager } from "./sdk/token";
+import { zeroFlorSub } from "./utils/math";
 
 export function handleAccrueInterest(event: AccrueInterest): void {
   const market = getMarket(event.params.id);
@@ -237,7 +238,7 @@ export function handleRepay(event: Repay): void {
     event.params.shares
   );
 
-  market.totalBorrow = market.totalBorrow.minus(event.params.assets);
+  market.totalBorrow = zeroFlorSub(market.totalBorrow, event.params.assets);
   market.totalBorrowShares = market.totalBorrowShares.minus(
     event.params.shares
   );
diff --git a/src/sdk/position.ts b/src/sdk/position.ts
index dbf1bc2..fd549c0 100644
--- a/src/sdk/position.ts
+++ b/src/sdk/position.ts
@@ -9,6 +9,7 @@ import {
 } from "../../generated/schema";
 import { getProtocol } from "../initializers/protocol";
 import { toAssetsDown, toAssetsUp } from "../maths/shares";
+import { zeroFlorSub } from "../utils/math";
 
 import {
   exponentToBigDecimal,
@@ -58,6 +59,7 @@ export class PositionManager {
 
     return Position.load(positionID);
   }
+
   addCollateralPosition(
     event: ethereum.Event,
     amountSupplied: BigInt
@@ -273,11 +275,8 @@ export class PositionManager {
     );
 
     position.balance = totalBorrow;
-    if (position.principal! > amountRepaid) {
-      position.principal = position.principal!.minus(amountRepaid);
-    } else {
-      position.principal = BigInt.zero();
-    }
+    position.principal = zeroFlorSub(position.principal!, amountRepaid);
+
     position.repayCount += 1;
 
     if (position.shares!.equals(BigInt.zero())) {
diff --git a/src/utils/math.ts b/src/utils/math.ts
new file mode 100644
index 0000000..02d36ec
--- /dev/null
+++ b/src/utils/math.ts
@@ -0,0 +1,8 @@
+import { BigInt } from "@graphprotocol/graph-ts";
+
+export const zeroFlorSub = (a: BigInt, b: BigInt): BigInt => {
+  if (a.lt(b)) {
+    return BigInt.zero();
+  }
+  return a.minus(b);
+};