diff --git a/packages/sdk/src/core/account.service.ts b/packages/sdk/src/core/account.service.ts
index ecd9f2c..b28c100 100644
--- a/packages/sdk/src/core/account.service.ts
+++ b/packages/sdk/src/core/account.service.ts
@@ -226,6 +226,10 @@ export class AccountService {
     secret: Secret;
     precommitment: Hash;
   } {
+    if(index && index < 0n) {
+      throw AccountError.invalidIndex(index);
+    }
+
     const accounts = this.account.poolAccounts.get(scope);
     index = index || BigInt(accounts?.length || 0);
 
diff --git a/packages/sdk/src/errors/account.error.ts b/packages/sdk/src/errors/account.error.ts
index da0a7dd..9e14d01 100644
--- a/packages/sdk/src/errors/account.error.ts
+++ b/packages/sdk/src/errors/account.error.ts
@@ -32,4 +32,11 @@ export class AccountError extends SDKError {
       ErrorCode.OPERATION_FAILED,
     );
   }
+
+  public static invalidIndex(index: bigint): AccountError {
+    return new AccountError(
+      `Invalid index: ${index.toString()}`,
+      ErrorCode.INVALID_INPUT,
+    );
+  }
 } 
\ No newline at end of file