diff --git a/package-lock.json b/package-lock.json
index 19acd8a0..36609115 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -4055,13 +4055,21 @@
       }
     },
     "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==",
+      "version": "0.6.0",
+      "resolved": "https://registry.npmjs.org/downlevel-dts/-/downlevel-dts-0.6.0.tgz",
+      "integrity": "sha512-Jy3ZZcXWPzTn5jJRW5WpdEtIq8+UowWWi5TEBgHHvzw320kouV//2KgVhfcuOpP93KS3UAokTxnZKU4L75kRSQ==",
       "dev": true,
       "requires": {
         "shelljs": "^0.8.3",
-        "typescript": "^3.8.0-dev.20200111"
+        "typescript": "^4.1.0-dev.20200804"
+      },
+      "dependencies": {
+        "typescript": {
+          "version": "4.1.0-dev.20200813",
+          "resolved": "https://registry.npmjs.org/typescript/-/typescript-4.1.0-dev.20200813.tgz",
+          "integrity": "sha512-P4X3A2rhq4WivVwKSwKNPqDCX/KfsSKuOykbEaWXiGT1c0fj/c14WCu4IOZ8USUp3rMhWfWySOYYi3Yzws8gGg==",
+          "dev": true
+        }
       }
     },
     "duplexer": {
diff --git a/package.json b/package.json
index 547659d2..fd1827a8 100644
--- a/package.json
+++ b/package.json
@@ -22,7 +22,7 @@
     "/ts3.4/"
   ],
   "scripts": {
-    "build": "tsc && downlevel-dts . ts3.4 && cp tsconfig.json ./ts3.4/",
+    "build": "tsc && rm -rf ./ts3.4 && downlevel-dts . ts3.4 && cp tsconfig.json ./ts3.4/",
     "build:watch": "tsc --watch",
     "build:babel-test": "babel src/test/lib/decorators_test.ts --out-file test/lib/decorators-babel_test.js",
     "gen-docs": "typedoc src/lit-element.ts src/lib/updating-element.ts",
@@ -49,7 +49,7 @@
     "@webcomponents/webcomponentsjs": "^2.2.3",
     "chai": "^4.0.2",
     "clang-format": "^1.2.4",
-    "downlevel-dts": "^0.4.0",
+    "downlevel-dts": "^0.6.0",
     "lit-element-benchmarks": "^0.1.0",
     "mocha": "^6.2.2",
     "np": "^5.2.1",