diff --git a/lib/parsers/gjs-gts-parser.js b/lib/parsers/gjs-gts-parser.js
index e23be687d6..849a078e1f 100644
--- a/lib/parsers/gjs-gts-parser.js
+++ b/lib/parsers/gjs-gts-parser.js
@@ -27,10 +27,9 @@ module.exports = {
     const isTypescript = options.filePath.endsWith('.gts');
 
     let result = null;
-    let filePath = options.filePath;
+    const filePath = options.filePath;
     if (options.project) {
       jsCode = replaceExtensions(jsCode);
-      filePath = options.filePath.replace(/\.gts$/, '.ts');
     }
 
     result = isTypescript
@@ -44,6 +43,19 @@ module.exports = {
     const visitorKeys = { ...result.visitorKeys, ...templateVisitorKeys };
     result.isTypescript = isTypescript;
     convertAst(result, preprocessedResult, visitorKeys);
+    if (result.services?.program) {
+      const sourceFiles = result.services?.program.getSourceFiles();
+      for (const sourceFile of sourceFiles) {
+        if (sourceFile.path.endsWith('.gts')) {
+          const mtsSourceFile = result.services?.program.getSourceFile(
+            sourceFile.path.replace(/\.gts$/, '.mts')
+          );
+          if (mtsSourceFile) {
+            Object.assign(mtsSourceFile, sourceFile);
+          }
+        }
+      }
+    }
     return { ...result, visitorKeys };
   },
 };
diff --git a/lib/parsers/ts-utils.js b/lib/parsers/ts-utils.js
index ef2d5761ac..5de91927c6 100644
--- a/lib/parsers/ts-utils.js
+++ b/lib/parsers/ts-utils.js
@@ -5,31 +5,38 @@ const babel = require('@babel/core');
 const { replaceRange } = require('./transform');
 
 module.exports.patchTs = function patchTs() {
-  const readDirectory = ts.sys.readDirectory;
-  ts.sys.readDirectory = function (...args) {
-    const results = readDirectory.call(this, ...args);
-    return results.map((f) => f.replace(/\.gts$/, '.ts'));
-  };
-  ts.sys.fileExists = function (fileName) {
-    return fs.existsSync(fileName.replace(/\.mts$/, '.gts')) || fs.existsSync(fileName);
-  };
-  ts.sys.readFile = function (fname) {
-    let fileName = fname;
-    let content = '';
-    try {
-      content = fs.readFileSync(fileName).toString();
-    } catch {
-      fileName = fileName.replace(/\.mts$/, '.gts');
-      content = fs.readFileSync(fileName).toString();
-    }
-    if (fileName.endsWith('.gts')) {
-      content = transformForLint(content).output;
-    }
-    if (fileName.endsWith('.ts') || fileName.endsWith('.gts')) {
-      content = replaceExtensions(content);
-    }
-    return content;
+  const sys = { ...ts.sys };
+  const newSys = {
+    ...ts.sys,
+    readDirectory(...args) {
+      const results = sys.readDirectory.call(this, ...args);
+      return [
+        ...results,
+        ...results.filter((x) => x.endsWith('.gts')).map((f) => f.replace(/\.gts$/, '.mts')),
+      ];
+    },
+    fileExists(fileName) {
+      return fs.existsSync(fileName.replace(/\.mts$/, '.gts')) || fs.existsSync(fileName);
+    },
+    readFile(fname) {
+      let fileName = fname;
+      let content = '';
+      try {
+        content = fs.readFileSync(fileName).toString();
+      } catch {
+        fileName = fileName.replace(/\.mts$/, '.gts');
+        content = fs.readFileSync(fileName).toString();
+      }
+      if (fileName.endsWith('.gts')) {
+        content = transformForLint(content).output;
+      }
+      if ((!fileName.endsWith('.d.ts') && fileName.endsWith('.ts')) || fileName.endsWith('.gts')) {
+        content = replaceExtensions(content);
+      }
+      return content;
+    },
   };
+  ts.setSys(newSys);
 };
 
 function replaceExtensions(code) {
diff --git a/package.json b/package.json
index e201afe148..01f037bcdc 100644
--- a/package.json
+++ b/package.json
@@ -84,8 +84,7 @@
     "lodash.camelcase": "^4.3.0",
     "lodash.kebabcase": "^4.1.1",
     "requireindex": "^1.2.0",
-    "snake-case": "^3.0.3",
-    "typescript": "^5.2.2"
+    "snake-case": "^3.0.3"
   },
   "devDependencies": {
     "@babel/plugin-proposal-class-properties": "^7.18.6",
@@ -114,7 +113,8 @@
     "npm-run-all": "^4.1.5",
     "prettier": "^3.0.3",
     "release-it": "^16.2.1",
-    "sort-package-json": "^2.6.0"
+    "sort-package-json": "^2.6.0",
+    "typescript": "^5.2.2"
   },
   "peerDependencies": {
     "eslint": ">= 8",
diff --git a/tests/lib/rules-preprocessor/gjs-gts-parser-test.js b/tests/lib/rules-preprocessor/gjs-gts-parser-test.js
index eb8624129f..a98e296bd7 100644
--- a/tests/lib/rules-preprocessor/gjs-gts-parser-test.js
+++ b/tests/lib/rules-preprocessor/gjs-gts-parser-test.js
@@ -9,6 +9,8 @@
 
 const { ESLint } = require('eslint');
 const plugin = require('../../../lib');
+const { writeFileSync, readFileSync } = require('node:fs');
+const { join } = require('node:path');
 
 const gjsGtsParser = require.resolve('../../../lib/parsers/gjs-gts-parser');
 
@@ -388,18 +390,28 @@ const invalid = [
     code: `
       import Component from '@glimmer/component';
 
+      const foo: any = '';
+
       export default class MyComponent extends Component {
         foo = 'bar';
 
         <template>
           <div></div>${'  '}
+          {{foo}}
         </template>
       }`,
     errors: [
+      {
+        message: 'Unexpected any. Specify a different type.',
+        line: 4,
+        endLine: 4,
+        column: 18,
+        endColumn: 21,
+      },
       {
         message: 'Trailing spaces not allowed.',
-        line: 8,
-        endLine: 8,
+        line: 10,
+        endLine: 10,
         column: 22,
         endColumn: 24,
       },
@@ -827,12 +839,12 @@ describe('multiple tokens in same file', () => {
       },
     });
 
-    const results = await eslint.lintFiles(['**/*.gts', '**/*.ts']);
+    let results = await eslint.lintFiles(['**/*.gts', '**/*.ts']);
 
-    const resultErrors = results.flatMap((result) => result.messages);
+    let resultErrors = results.flatMap((result) => result.messages);
     expect(resultErrors).toHaveLength(3);
 
-    expect(resultErrors[0].message).toBe("Use 'String#startsWith' method instead."); // Actual result is "Unsafe member access [0] on an `any` value."
+    expect(resultErrors[0].message).toBe("Use 'String#startsWith' method instead.");
     expect(resultErrors[0].line).toBe(6);
 
     expect(resultErrors[1].line).toBe(7);
@@ -840,5 +852,38 @@ describe('multiple tokens in same file', () => {
 
     expect(resultErrors[2].line).toBe(8);
     expect(resultErrors[2].message).toBe("Use 'String#startsWith' method instead.");
+
+    const filePath = join(__dirname, 'ember_ts', 'bar.gts');
+    const content = readFileSync(filePath).toString();
+    try {
+      writeFileSync(filePath, content.replace("'42'", '42'));
+
+      results = await eslint.lintFiles(['**/*.gts', '**/*.ts']);
+
+      resultErrors = results.flatMap((result) => result.messages);
+      expect(resultErrors).toHaveLength(2);
+
+      expect(resultErrors[0].message).toBe("Use 'String#startsWith' method instead.");
+      expect(resultErrors[0].line).toBe(6);
+
+      expect(resultErrors[1].line).toBe(8);
+      expect(resultErrors[1].message).toBe("Use 'String#startsWith' method instead.");
+    } finally {
+      writeFileSync(filePath, content);
+    }
+
+    results = await eslint.lintFiles(['**/*.gts', '**/*.ts']);
+
+    resultErrors = results.flatMap((result) => result.messages);
+    expect(resultErrors).toHaveLength(3);
+
+    expect(resultErrors[0].message).toBe("Use 'String#startsWith' method instead.");
+    expect(resultErrors[0].line).toBe(6);
+
+    expect(resultErrors[1].message).toBe("Use 'String#startsWith' method instead.");
+    expect(resultErrors[1].line).toBe(7);
+
+    expect(resultErrors[2].line).toBe(8);
+    expect(resultErrors[2].message).toBe("Use 'String#startsWith' method instead.");
   });
 });
diff --git a/tests/lib/rules-preprocessor/tsconfig.eslint.json b/tests/lib/rules-preprocessor/tsconfig.eslint.json
index 23f2d756df..b58959351c 100644
--- a/tests/lib/rules-preprocessor/tsconfig.eslint.json
+++ b/tests/lib/rules-preprocessor/tsconfig.eslint.json
@@ -5,6 +5,7 @@
     "strictNullChecks": true
   },
   "include": [
-    "**/*"
+    "**/*.ts",
+    "**/*.gts"
   ],
 }