diff --git a/src/contractBatch/aggregate.ts b/src/contractBatch/aggregate.ts
index d4aa2f0..80ce020 100644
--- a/src/contractBatch/aggregate.ts
+++ b/src/contractBatch/aggregate.ts
@@ -21,12 +21,12 @@ const partitionResponses = (responses: string[]): string[][] => {
   return [response, ...partitionResponses(remainingResponses)]
 }
 
-const extractErrorCallIndex = (e: Error) => {
+export const extractErrorCallIndex = (e: Error) => {
   try {
     const errorCallText = e.toString()
 
     const sequencerErrorIndex = errorCallText.match(
-      /Error message: multicall (\d+) failed/,
+      /Error message: multicall (\d+).*failed/,
     )?.[1]
     if (sequencerErrorIndex) {
       return Number(sequencerErrorIndex)
diff --git a/src/contractBatch/unit.test.ts b/src/contractBatch/unit.test.ts
index 0c09760..1f2311b 100644
--- a/src/contractBatch/unit.test.ts
+++ b/src/contractBatch/unit.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, mock, test } from "bun:test"
 import { ContractBatchProvider } from "./ContractBatchProvider"
 import { MinimalProviderInterface } from "../types"
+import { extractErrorCallIndex } from "./aggregate.ts"
 
 function getMockProvider(responses: string[][]): MinimalProviderInterface {
   const blockNumber = "0x1"
@@ -56,3 +57,27 @@ describe("ContractBatchProvider", () => {
     expect(provider.callContract).toHaveBeenCalledTimes(1)
   })
 })
+
+describe("extractErrorCallIndex", () => {
+  test("should extract call index from error message", () => {
+    const error = new Error("Error message: multicall 5 failed")
+    const result = extractErrorCallIndex(error)
+    expect(result).toBe(5)
+  })
+
+  test("should extract call index from error message with colon ", () => {
+    const error = new Error("Error message: multicall 12:300 failed")
+    const result = extractErrorCallIndex(error)
+    expect(result).toBe(12)
+  })
+
+  test("should throw error when pattern doesn't match", () => {
+    const error = new Error("Some other error message")
+    expect(() => extractErrorCallIndex(error)).toThrow()
+  })
+
+  test("should throw error when no index is present", () => {
+    const error = new Error("Error message: multicall failed")
+    expect(() => extractErrorCallIndex(error)).toThrow()
+  })
+})