diff --git a/packages/angular_devkit/build_optimizer/package.json b/packages/angular_devkit/build_optimizer/package.json
index a0bba9a9b6..ffa50a91a2 100644
--- a/packages/angular_devkit/build_optimizer/package.json
+++ b/packages/angular_devkit/build_optimizer/package.json
@@ -12,7 +12,7 @@
     "loader-utils": "1.4.0",
     "source-map": "0.7.3",
     "tslib": "1.11.1",
-    "typescript": "3.6.4",
+    "typescript": "3.8.2",
     "webpack-sources": "1.4.3"
   }
 }
diff --git a/packages/angular_devkit/build_optimizer/src/transforms/scrub-file.ts b/packages/angular_devkit/build_optimizer/src/transforms/scrub-file.ts
index 628c41b0e8..fe3718003e 100644
--- a/packages/angular_devkit/build_optimizer/src/transforms/scrub-file.ts
+++ b/packages/angular_devkit/build_optimizer/src/transforms/scrub-file.ts
@@ -594,7 +594,7 @@ function isTslibHelper(
   checker: ts.TypeChecker,
 ) {
 
-  let callExprIdent = callExpr.expression as ts.Identifier;
+  let callExprIdent = callExpr.expression as ts.Identifier | ts.PrivateIdentifier;
 
   if (callExpr.expression.kind !== ts.SyntaxKind.Identifier) {
     if (callExpr.expression.kind === ts.SyntaxKind.PropertyAccessExpression) {
diff --git a/yarn.lock b/yarn.lock
index 177b376416..5d5c370a2e 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -11482,11 +11482,6 @@ typedarray@^0.0.6:
   resolved "https://registry.yarnpkg.com/typedarray/-/typedarray-0.0.6.tgz#867ac74e3864187b1d3d47d996a78ec5c8830777"
   integrity sha1-hnrHTjhkGHsdPUfZlqeOxciDB3c=
 
-typescript@3.6.4:
-  version "3.6.4"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.6.4.tgz#b18752bb3792bc1a0281335f7f6ebf1bbfc5b91d"
-  integrity sha512-unoCll1+l+YK4i4F8f22TaNVPRHcD9PA3yCuZ8g5e0qGqlVlJ/8FSateOLLSagn+Yg5+ZwuPkL8LFUc0Jcvksg==
-
 typescript@3.8.2:
   version "3.8.2"
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.8.2.tgz#91d6868aaead7da74f493c553aeff76c0c0b1d5a"