diff --git a/package-lock.json b/package-lock.json
index b2173a7..1318fc2 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1553,6 +1553,25 @@
         }
       }
     },
+    "downlevel-dts": {
+      "version": "0.10.0",
+      "resolved": "https://registry.npmjs.org/downlevel-dts/-/downlevel-dts-0.10.0.tgz",
+      "integrity": "sha512-AZ7tnUy4XJArsjv6Bcuivvxx+weMvOGHF6seu7e7PVOqMDHMSlfgMl1kt+F4Y2+5TmDwKWHOdimM1DZKihQs8Q==",
+      "dev": true,
+      "requires": {
+        "semver": "^7.3.2",
+        "shelljs": "^0.8.3",
+        "typescript": "^4.8.0-dev.20220719"
+      },
+      "dependencies": {
+        "typescript": {
+          "version": "4.8.0-dev.20220719",
+          "resolved": "https://registry.npmjs.org/typescript/-/typescript-4.8.0-dev.20220719.tgz",
+          "integrity": "sha512-IAZp6IDszN9iZi7R5LOqR5j0Ffy737RVQF7IefH1hNtFE+HiTjfsEYtWD2M0X/2feOCESZEKaa+GmuOVFuFhUQ==",
+          "dev": true
+        }
+      }
+    },
     "eastasianwidth": {
       "version": "0.2.0",
       "resolved": "https://registry.npmjs.org/eastasianwidth/-/eastasianwidth-0.2.0.tgz",
@@ -2297,6 +2316,12 @@
       "integrity": "sha512-k/vGaX4/Yla3WzyMCvTQOXYeIHvqOKtnqBduzTHpzpQZzAskKMhZ2K+EnBiSM9zGSoIFeMpXKxa4dYeZIQqewQ==",
       "dev": true
     },
+    "interpret": {
+      "version": "1.4.0",
+      "resolved": "https://registry.npmjs.org/interpret/-/interpret-1.4.0.tgz",
+      "integrity": "sha512-agE4QfB2Lkp9uICn7BAqoscw4SZP9kTE2hxiFI3jBPmXJfdqiahTbUuKGsMoN2GtqL9AxhYioAcVvgsb1HvRbA==",
+      "dev": true
+    },
     "irregular-plurals": {
       "version": "3.3.0",
       "resolved": "https://registry.npmjs.org/irregular-plurals/-/irregular-plurals-3.3.0.tgz",
@@ -3410,6 +3435,15 @@
         "picomatch": "^2.2.1"
       }
     },
+    "rechoir": {
+      "version": "0.6.2",
+      "resolved": "https://registry.npmjs.org/rechoir/-/rechoir-0.6.2.tgz",
+      "integrity": "sha512-HFM8rkZ+i3zrV+4LQjwQ0W+ez98pApMGM3HUrN04j3CqzPOzl9nmP15Y8YXNm8QHGv/eacOVEjqhmWpkRV0NAw==",
+      "dev": true,
+      "requires": {
+        "resolve": "^1.1.6"
+      }
+    },
     "regexpp": {
       "version": "3.2.0",
       "resolved": "https://registry.npmjs.org/regexpp/-/regexpp-3.2.0.tgz",
@@ -3645,6 +3679,17 @@
       "integrity": "sha512-7++dFhtcx3353uBaq8DDR4NuxBetBzC7ZQOhmTQInHEd6bSrXdiEyzCvG07Z44UYdLShWUyXt5M/yhz8ekcb1A==",
       "dev": true
     },
+    "shelljs": {
+      "version": "0.8.5",
+      "resolved": "https://registry.npmjs.org/shelljs/-/shelljs-0.8.5.tgz",
+      "integrity": "sha512-TiwcRcrkhHvbrZbnRcFYMLl30Dfov3HKqzp5tO5b4pt6G/SezKcYhmDg15zXVBswHmctSAQKznqNW2LO5tTDow==",
+      "dev": true,
+      "requires": {
+        "glob": "^7.0.0",
+        "interpret": "^1.0.0",
+        "rechoir": "^0.6.2"
+      }
+    },
     "signal-exit": {
       "version": "3.0.6",
       "resolved": "https://registry.npmjs.org/signal-exit/-/signal-exit-3.0.6.tgz",
diff --git a/package.json b/package.json
index 62cd905..a209c05 100644
--- a/package.json
+++ b/package.json
@@ -4,9 +4,18 @@
   "description": "Rollup Sass files.",
   "main": "dist/index.js",
   "typings": "dist/index.d.ts",
+  "typesVersions": {
+    "<4.0": {
+      "*": [
+        "ts3.5/*"
+      ]
+    }
+  },
   "scripts": {
     "prepare": "npm run build && npm test",
-    "build": "tsc --project tsconfig.json",
+    "build": "npm run build-downlevel-dts && tsc --project tsconfig.json",
+    "build-downlevel-dts": "node scripts/clean-and-run-downlevel-dts.js",
+    "downlevel-dts": "downlevel-dts . ts3.5 [--to=3.5]",
     "test": "nyc --reporter=html --reporter=text ava ./test/*.test.ts -s && npm run test:rollup.config.spec.ts",
     "coverage": "nyc report --reporter=text-lcov | coveralls",
     "test:rollup.config.spec.ts": "tsc --project tsconfig.spec.json --noEmit"
@@ -59,6 +68,7 @@
     "@types/sass": "^1.16.1",
     "ava": "^4.3.1",
     "coveralls": "^3.1.1",
+    "downlevel-dts": "^0.10.0",
     "eslint": "^7.32.0",
     "jsdom": "^17.0.0",
     "nyc": "^15.1.0",
diff --git a/scripts/clean-and-run-downlevel-dts.js b/scripts/clean-and-run-downlevel-dts.js
new file mode 100644
index 0000000..9bd9b93
--- /dev/null
+++ b/scripts/clean-and-run-downlevel-dts.js
@@ -0,0 +1,47 @@
+/**
+ * @script clean-and-run-downlevel-dts.js
+ * @description Removes '{repo-root}/ts3.5' directory, re-creates it, runs
+ *  `npm run downlevel-dts` from repo-root, and copies the root tsconfig.json file into new directory.
+ */
+ const fs = require('fs').promises,
+  path = require('path'),
+  {spawn} = require('child_process'),
+
+  {log, warn, error} = console,
+
+  rootDir = path.join(__dirname, '..'),
+  outputDir = path.resolve(path.join(__dirname, '../ts3.5')),
+
+  tsConfigFilePath = path.join(rootDir, 'tsconfig.json'),
+  tsConfigOutFilePath = path.join(outputDir, 'tsconfig.json');
+
+(async () =>
+    fs.rmdir(outputDir, {recursive: true})
+
+      .then(() => fs.mkdir(outputDir))
+
+      .then(() => fs.copyFile(tsConfigFilePath, tsConfigOutFilePath))
+
+      // Run downlevel-dts
+      .then(() => new Promise((resolve, reject) => {
+
+        // Start downlevel-dts package script
+        const subProcess = spawn('npm', ['run', 'downlevel-dts'], {cwd: rootDir});
+
+        // Log child process buffer data as `string`
+        subProcess.stdout.on('data', data => log(data.toString().trim() + '\n'));
+
+        // Log stderr, child process, buffer data as a `string`
+        subProcess.stderr.on('data', data => warn(data.toString().trim() + '\n'));
+
+        // Handle process end
+        subProcess.on('close', (code) => code !== 0 ?
+          reject(`Child process existed with code ${code}.\n`) :
+          resolve('Process completed successfully.\n')
+        );
+
+        // Catch process start errors
+        subProcess.on('error', reject);
+      }))
+
+)().then(log, error);