diff --git a/docs/CodeTransformation.md b/docs/CodeTransformation.md
index 2d16208eb10f..3be3e0ac9a0e 100644
--- a/docs/CodeTransformation.md
+++ b/docs/CodeTransformation.md
@@ -40,7 +40,7 @@ interface TransformOptions<TransformerConfig = unknown> {
   supportsTopLevelAwait: boolean;
   instrument: boolean;
   /** Cached file system which is used by `jest-runtime` to improve performance. */
-  cacheFS: Map<string, string>;
+  cacheFS: Map<string, Buffer | string>;
   /** Jest configuration of currently running project. */
   config: ProjectConfig;
   /** Stringified version of the `config` - useful in cache busting. */
diff --git a/packages/babel-jest/src/__tests__/index.ts b/packages/babel-jest/src/__tests__/index.ts
index 9903c2b773b0..4808bd0e591a 100644
--- a/packages/babel-jest/src/__tests__/index.ts
+++ b/packages/babel-jest/src/__tests__/index.ts
@@ -52,7 +52,7 @@ test('Returns source string with inline maps when no transformOptions is passed'
     sourceString,
     'dummy_path.js',
     {
-      cacheFS: new Map<string, string>(),
+      cacheFS: new Map<string, Buffer | string>(),
       config: makeProjectConfig(),
       configString: JSON.stringify(makeProjectConfig()),
       instrument: false,
@@ -76,7 +76,7 @@ test('Returns source string with inline maps when no transformOptions is passed
     sourceString,
     'dummy_path.js',
     {
-      cacheFS: new Map<string, string>(),
+      cacheFS: new Map<string, Buffer | string>(),
       config: makeProjectConfig(),
       configString: JSON.stringify(makeProjectConfig()),
       instrument: false,
@@ -141,7 +141,7 @@ describe('caller option correctly merges from defaults and options', () => {
     ],
   ])('%j -> %j', (input, output) => {
     defaultBabelJestTransformer.process(sourceString, 'dummy_path.js', {
-      cacheFS: new Map<string, string>(),
+      cacheFS: new Map<string, Buffer | string>(),
       config: makeProjectConfig(),
       configString: JSON.stringify(makeProjectConfig()),
       instrument: false,
@@ -166,7 +166,7 @@ describe('caller option correctly merges from defaults and options', () => {
 test('can pass null to createTransformer', () => {
   const transformer = createTransformer();
   transformer.process(sourceString, 'dummy_path.js', {
-    cacheFS: new Map<string, string>(),
+    cacheFS: new Map<string, Buffer | string>(),
     config: makeProjectConfig(),
     configString: JSON.stringify(makeProjectConfig()),
     instrument: false,
diff --git a/packages/jest-repl/src/cli/repl.ts b/packages/jest-repl/src/cli/repl.ts
index 3a486c6bfbb7..aceb9f1fb180 100644
--- a/packages/jest-repl/src/cli/repl.ts
+++ b/packages/jest-repl/src/cli/repl.ts
@@ -33,7 +33,7 @@ const evalCommand: repl.REPLEval = (
         cmd,
         jestGlobalConfig.replname ?? 'jest.js',
         {
-          cacheFS: new Map<string, string>(),
+          cacheFS: new Map<string, Buffer | string>(),
           config: jestProjectConfig,
           configString: JSON.stringify(jestProjectConfig),
           instrument: false,
diff --git a/packages/jest-runtime/src/index.ts b/packages/jest-runtime/src/index.ts
index ed0d5f9e50c2..5941ec3076db 100644
--- a/packages/jest-runtime/src/index.ts
+++ b/packages/jest-runtime/src/index.ts
@@ -153,7 +153,7 @@ const supportsNodeColonModulePrefixInRequire = (() => {
 })();
 
 export default class Runtime {
-  private readonly _cacheFS: Map<string, string>;
+  private readonly _cacheFS: Map<string, Buffer | string>;
   private readonly _config: Config.ProjectConfig;
   private readonly _globalConfig?: Config.GlobalConfig;
   private readonly _coverageOptions: ShouldInstrumentOptions;
@@ -211,7 +211,7 @@ export default class Runtime {
     environment: JestEnvironment,
     resolver: Resolver,
     transformer: ScriptTransformer,
-    cacheFS: Map<string, string>,
+    cacheFS: Map<string, Buffer | string>,
     coverageOptions: ShouldInstrumentOptions,
     testPath: string,
     // TODO: make mandatory in Jest 30
@@ -446,7 +446,7 @@ export default class Runtime {
 
       if (modulePath.endsWith('.wasm')) {
         const wasm = this._importWasmModule(
-          fs.readFileSync(modulePath),
+          this.readFileBuffer(modulePath),
           modulePath,
           context,
         );
@@ -2376,6 +2376,23 @@ export default class Runtime {
     };
   }
 
+  private readFileBuffer(filename: string): Buffer {
+    let source = this._cacheFS.get(filename);
+
+    if (!source) {
+      source = fs.readFileSync(filename);
+
+      this._cacheFS.set(filename, source);
+    }
+
+    if (typeof source === 'string') {
+      // This may occur if readFileBuffer and readFile are called interchangeably for one file
+      throw new Error("Expected source to be a 'Buffer', but got 'string'");
+    }
+
+    return source;
+  }
+
   private readFile(filename: string): string {
     let source = this._cacheFS.get(filename);
 
@@ -2385,6 +2402,11 @@ export default class Runtime {
       this._cacheFS.set(filename, source);
     }
 
+    if (typeof source !== 'string') {
+      // This may occur if readFileBuffer and readFile are called interchangeably for one file
+      throw new Error("Expected source to be a 'string', but got 'Buffer'");
+    }
+
     return source;
   }