diff --git a/package.json b/package.json
index 00b0b77..e639d49 100644
--- a/package.json
+++ b/package.json
@@ -79,9 +79,9 @@
     "@jsdevtools/coverage-istanbul-loader": "^3.0.5",
     "@types/istanbul-lib-coverage": "^2.0.4",
     "convert-source-map": "^2.0.0",
+    "espree": "^9.6.1",
     "istanbul-lib-instrument": "^6.0.1",
-    "loader-utils": "^3.2.1",
-    "merge-source-map": "^1.1.0",
+    "source-map": "^0.7.4",
     "test-exclude": "^6.0.0",
     "vite-plugin-istanbul": "^3.0.1"
   }
diff --git a/src/loader/webpack5-istanbul-loader.ts b/src/loader/webpack5-istanbul-loader.ts
index 0e08dc9..2d21da7 100644
--- a/src/loader/webpack5-istanbul-loader.ts
+++ b/src/loader/webpack5-istanbul-loader.ts
@@ -1,16 +1,19 @@
+import { Instrumenter, InstrumenterOptions } from "istanbul-lib-instrument";
 import { fromSource, fromMapFileSource } from "convert-source-map";
-import {
-  createInstrumenter,
-  InstrumenterOptions,
-} from "istanbul-lib-instrument";
+
 // @ts-expect-error no types
-import mergeSourceMap from "merge-source-map";
-import { LoaderContext } from "webpack";
+import * as espree from "espree";
 import fs from "fs";
 import path from "path";
+import { LoaderContext } from "webpack";
+import { SourceMapGenerator, StartOfSourceMap } from "source-map";
+
 import { AddonOptionsWebpack } from "../types";
 
-export type Options = Partial<InstrumenterOptions> & AddonOptionsWebpack;
+export type Options = Partial<InstrumenterOptions> &
+  AddonOptionsWebpack & {
+    instrumenter: Instrumenter;
+  };
 
 type RawSourceMap = {
   version: number;
@@ -22,51 +25,74 @@ type RawSourceMap = {
   names?: string[];
 };
 
-export const defaultOptions: Partial<InstrumenterOptions> = {
-  preserveComments: true,
-  produceSourceMap: true,
-  autoWrap: true,
-  esModules: true,
-  compact: false,
-};
+function sanitizeSourceMap(rawSourceMap: RawSourceMap): RawSourceMap {
+  const { sourcesContent, ...sourceMap } = rawSourceMap ?? {};
+
+  // JSON parse/stringify trick required for istanbul to accept the SourceMap
+  return JSON.parse(JSON.stringify(sourceMap));
+}
+
+function createIdentitySourceMap(
+  file: string,
+  source: string,
+  option: StartOfSourceMap
+) {
+  const gen = new SourceMapGenerator(option);
+  const tokens = espree.tokenize(source, { loc: true, ecmaVersion: "latest" });
+
+  tokens.forEach((token: any) => {
+    const loc = token.loc.start;
+    gen.addMapping({
+      source: file,
+      original: loc,
+      generated: loc,
+    });
+  });
+
+  return JSON.parse(gen.toString());
+}
 
 export default function (
   this: LoaderContext<Options>,
   source: string,
   sourceMap?: RawSourceMap
 ) {
-  let map = sourceMap;
-  let options = Object.assign(defaultOptions, this.getOptions());
+  let map = sourceMap ?? getInlineSourceMap.call(this, source);
+  const options = this.getOptions();
+  const callback = this.async();
 
-  // If there's no external sourceMap file, then check for an inline sourceMap
   if (!map) {
-    map = sourceMap = getInlineSourceMap.call(this, source);
+    callback(null, source, sourceMap);
+    return;
   }
 
   // Instrument the code
-  let instrumenter = createInstrumenter(options);
-  instrumenter.instrument(
+  const instrumenter = options.instrumenter;
+
+  const combinedSourceMap = sanitizeSourceMap(sourceMap);
+
+  const code = instrumenter.instrumentSync(
     source,
     this.resourcePath,
-    (error, instrumentedSource) => {
-      let instrumentedSourceMap = instrumenter.lastSourceMap();
-
-      if (sourceMap && instrumentedSourceMap) {
-        // Re-map the source map to the original source code
-        instrumentedSourceMap = mergeSourceMap(
-          sourceMap,
-          instrumentedSourceMap
-        );
-      }
-
-      this.callback(
-        error,
-        instrumentedSource,
-        instrumentedSourceMap as any as RawSourceMap
-      );
-    },
-    sourceMap as any
+    combinedSourceMap as any
+  );
+
+  const identitySourceMap = sanitizeSourceMap(
+    createIdentitySourceMap(this.resourcePath, source, {
+      file: combinedSourceMap.file,
+      sourceRoot: combinedSourceMap.sourceRoot,
+    })
   );
+
+  instrumenter.instrumentSync(
+    source,
+    this.resourcePath,
+    identitySourceMap as any
+  );
+
+  const lastSourceMap = instrumenter.lastSourceMap();
+
+  callback(null, code, lastSourceMap as any);
 }
 
 /**
diff --git a/src/preset.ts b/src/preset.ts
index 6af9b39..019ed29 100644
--- a/src/preset.ts
+++ b/src/preset.ts
@@ -3,6 +3,10 @@ import { defaultExclude, defaultExtensions } from "./constants";
 import type { AddonOptionsVite, AddonOptionsWebpack } from "./types";
 import { createTestExclude } from "./webpack5-exclude";
 import { getNycConfig } from "./nyc-config";
+import {
+  InstrumenterOptions,
+  createInstrumenter,
+} from "istanbul-lib-instrument";
 
 export const viteFinal = async (
   viteConfig: Record<string, any>,
@@ -32,6 +36,14 @@ export const viteFinal = async (
   return viteConfig;
 };
 
+const defaultOptions: Partial<InstrumenterOptions> = {
+  preserveComments: true,
+  produceSourceMap: true,
+  autoWrap: true,
+  esModules: true,
+  compact: false,
+};
+
 export const webpackFinal = async (
   webpackConfig: Record<string, any>,
   options: Options & AddonOptionsWebpack
@@ -45,11 +57,17 @@ export const webpackFinal = async (
 
   const testExclude = await createTestExclude(options.istanbul);
 
-  webpackConfig.module.rules.push({
+  let instrumenterOptions = Object.assign(defaultOptions, options.istanbul);
+  let instrumenter = createInstrumenter(instrumenterOptions);
+
+  webpackConfig.module.rules.unshift({
     test: new RegExp(extensions?.join("|").replace(/\./g, "\\.")),
     loader: require.resolve("./loader/webpack5-istanbul-loader"),
     enforce: "post",
-    options: options.istanbul || {},
+    options: {
+      ...(options.istanbul ?? {}),
+      instrumenter,
+    },
     include: (modulePath: string) => testExclude.shouldInstrument(modulePath),
   });
 
diff --git a/yarn.lock b/yarn.lock
index 829c8ce..91d0457 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1903,7 +1903,12 @@ acorn-import-assertions@^1.9.0:
   resolved "https://registry.yarnpkg.com/acorn-import-assertions/-/acorn-import-assertions-1.9.0.tgz#507276249d684797c84e0734ef84860334cfb1ac"
   integrity sha512-cmMwop9x+8KFhxvKrKfPYmN6/pKTYYHBqLa0DfvVZcKMJWNyWLnaqND7dx/qn66R7ewM1UX5XMaDVP5wlVTaVA==
 
-acorn@^8.7.1, acorn@^8.8.2:
+acorn-jsx@^5.3.2:
+  version "5.3.2"
+  resolved "https://registry.yarnpkg.com/acorn-jsx/-/acorn-jsx-5.3.2.tgz#7ed5bb55908b3b2f1bc55c6af1653bada7f07937"
+  integrity sha512-rq9s+JNhf0IChjtDXxllJ7g41oZk5SlXtp0LHwyA5cejwn7vKmKp4pPri6YEePv2PU65sAsegbXtIinmDFDXgQ==
+
+acorn@^8.7.1, acorn@^8.8.2, acorn@^8.9.0:
   version "8.11.2"
   resolved "https://registry.yarnpkg.com/acorn/-/acorn-8.11.2.tgz#ca0d78b51895be5390a5903c5b3bdcdaf78ae40b"
   integrity sha512-nc0Axzp/0FILLEVsm4fNwLCwMttvhEI263QtVPQcbpfZZ3ts0hLsZGOpE6czNlid7CJ9MlyH8reXkpsf3YUY4w==
@@ -3039,6 +3044,20 @@ eslint-scope@5.1.1:
     esrecurse "^4.3.0"
     estraverse "^4.1.1"
 
+eslint-visitor-keys@^3.4.1:
+  version "3.4.3"
+  resolved "https://registry.yarnpkg.com/eslint-visitor-keys/-/eslint-visitor-keys-3.4.3.tgz#0cd72fe8550e3c2eae156a96a4dddcd1c8ac5800"
+  integrity sha512-wpc+LXeiyiisxPlEkUzU6svyS1frIO3Mgxj1fdy7Pm8Ygzguax2N3Fa/D/ag1WqbOprdI+uY6wMUl8/a2G+iag==
+
+espree@^9.6.1:
+  version "9.6.1"
+  resolved "https://registry.yarnpkg.com/espree/-/espree-9.6.1.tgz#a2a17b8e434690a5432f2f8018ce71d331a48c6f"
+  integrity sha512-oruZaFkjorTpF32kDSI5/75ViwGeZginGGy2NoOSg3Q9bnwlnmDm4HLnkl0RE3n+njDXR037aY1+x58Z/zFdwQ==
+  dependencies:
+    acorn "^8.9.0"
+    acorn-jsx "^5.3.2"
+    eslint-visitor-keys "^3.4.1"
+
 esprima@^4.0.0:
   version "4.0.1"
   resolved "https://registry.yarnpkg.com/esprima/-/esprima-4.0.1.tgz#13b04cdb3e6c5d19df91ab6987a8695619b0aa71"
@@ -4045,11 +4064,6 @@ loader-utils@^2.0.0:
     emojis-list "^3.0.0"
     json5 "^2.1.2"
 
-loader-utils@^3.2.1:
-  version "3.2.1"
-  resolved "https://registry.yarnpkg.com/loader-utils/-/loader-utils-3.2.1.tgz#4fb104b599daafd82ef3e1a41fb9265f87e1f576"
-  integrity sha512-ZvFw1KWS3GVyYBYb7qkmRM/WwL2TQQBxgCK62rlvm4WpVQ23Nb4tYjApUlfjrEGvOs7KHEsmyUn75OHZrJMWPw==
-
 locate-path@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/locate-path/-/locate-path-2.0.0.tgz#2b568b265eec944c6d9c0de9c3dbbbca0354cd8e"
@@ -5282,6 +5296,11 @@ source-map@^0.6.0, source-map@^0.6.1:
   resolved "https://registry.yarnpkg.com/source-map/-/source-map-0.6.1.tgz#74722af32e9614e9c287a8d0bbde48b5e2f1a263"
   integrity sha512-UjgapumWlbMhkBgzT7Ykc5YXUT46F0iKu8SGXq0bcwP5dz/h0Plj6enJqjz1Zbq2l5WaqYnrVbwWOWMyF3F47g==
 
+source-map@^0.7.4:
+  version "0.7.4"
+  resolved "https://registry.yarnpkg.com/source-map/-/source-map-0.7.4.tgz#a9bbe705c9d8846f4e08ff6765acf0f1b0898656"
+  integrity sha512-l3BikUxvPOcn5E74dZiq5BGsTb5yEwhaTSzccU6t4sDOH8NWJCstKO5QT2CvtFoK6F0saL7p9xHAqHOlCPJygA==
+
 spawn-command@^0.0.2-1:
   version "0.0.2-1"
   resolved "https://registry.yarnpkg.com/spawn-command/-/spawn-command-0.0.2-1.tgz#62f5e9466981c1b796dc5929937e11c9c6921bd0"