diff --git a/.github/workflows/test_old_compile.yml b/.github/workflows/test_old_compile.yml
new file mode 100644
index 00000000..c366c11b
--- /dev/null
+++ b/.github/workflows/test_old_compile.yml
@@ -0,0 +1,29 @@
+name: Build in TSC 3.4
+
+on: [push, pull_request]
+
+
+jobs:
+  build_old:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v1
+        with:
+          node-version: 12
+
+      - name: NPM install
+        run: npm ci
+
+      - name: Build
+        run: npm run build
+
+      - name: Install typescript@~3.4
+        run: npm install typescript@~3.4
+
+      - name: Print TypeScript version
+        run: npx tsc --version
+
+      - name: Type check .d.ts files
+        run: npx tsc ts3.4/lit-element.d.ts --noEmit -t esnext --moduleResolution Node
diff --git a/.gitignore b/.gitignore
index 65d2bd7b..33d70f5a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,11 +1,13 @@
 /node_modules/
-/lib/
 
 #Compiler Output
-lit-element.js
-lit-element.js.map
-lit-element.d.ts
-lit-element.d.ts.map
+/lib/
+/ts3.4/
+
+/lit-element.js
+/lit-element.js.map
+/lit-element.d.ts
+/lit-element.d.ts.map
 
 /test/**/*.d.ts
 /test/**/*.d.ts.map
diff --git a/.npmignore b/.npmignore
index 35bfc4d9..e0c42a45 100644
--- a/.npmignore
+++ b/.npmignore
@@ -1 +1,10 @@
 docs/
+.travis.yml
+check-version-tracker.js
+rollup.config.js
+tslint.json
+tsconfig_apidoc.json
+wct.conf.json
+.vscode/
+.github/
+.clang-format
diff --git a/package-lock.json b/package-lock.json
index 14ee155f..91c2bf1f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "lit-element",
-  "version": "2.2.1",
+  "version": "2.3.0",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
@@ -4068,6 +4068,16 @@
         "is-obj": "^1.0.0"
       }
     },
+    "downlevel-dts": {
+      "version": "0.4.0",
+      "resolved": "https://registry.npmjs.org/downlevel-dts/-/downlevel-dts-0.4.0.tgz",
+      "integrity": "sha512-nh5vM3n2pRhPwZqh0iWo5gpItPAYEGEWw9yd0YpI+lO60B7A3A6iJlxDbt7kKVNbqBXKsptL+jwE/Yg5Go66WQ==",
+      "dev": true,
+      "requires": {
+        "shelljs": "^0.8.3",
+        "typescript": "^3.8.0-dev.20200111"
+      }
+    },
     "duplexer": {
       "version": "0.1.1",
       "resolved": "https://registry.npmjs.org/duplexer/-/duplexer-0.1.1.tgz",
diff --git a/package.json b/package.json
index e5698be0..4a6f56a0 100644
--- a/package.json
+++ b/package.json
@@ -21,7 +21,7 @@
     "/lit-element.js.map"
   ],
   "scripts": {
-    "build": "tsc",
+    "build": "tsc && downlevel-dts . ts3.4 && cp tsconfig.json ./ts3.4/",
     "build:babel-test": "babel src/test/lib/decorators_test.ts --out-file test/lib/decorators-babel_test.js",
     "gen-docs": "typedoc --readme docs/_api/api-readme.md --tsconfig tsconfig_apidoc.json --mode modules --theme docs/_api/theme --excludeNotExported --excludePrivate --ignoreCompilerErrors --exclude '{**/*test*,**/node_modules/**,**/test/**}' --out ./docs/api --gaID UA-39334307-23 src/**/*.ts",
     "test": "npm run build && npm run build:babel-test && wct",
@@ -46,6 +46,7 @@
     "@webcomponents/webcomponentsjs": "^2.2.3",
     "chai": "^4.0.2",
     "clang-format": "^1.2.4",
+    "downlevel-dts": "^0.4.0",
     "lit-element-benchmarks": "^0.1.0",
     "mocha": "^6.2.2",
     "np": "^5.2.1",
@@ -56,12 +57,19 @@
     "tachometer": "^0.4.16",
     "tslint": "^5.20.1",
     "typedoc": "^0.14.2",
-    "typescript": "^3.8.2",
+    "typescript": "~3.8.2",
     "uglify-es": "^3.3.9",
     "wct-mocha": "^1.0.0",
     "web-component-tester": "^6.9.2"
   },
   "typings": "lit-element.d.ts",
+  "typesVersions": {
+    "<3.8": {
+      "*": [
+        "ts3.4/*"
+      ]
+    }
+  },
   "dependencies": {
     "lit-html": "^1.1.1"
   },