diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 2ec11d92..77200b8a 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -4,6 +4,7 @@
   * [Getting Code](#getting-code)
   * [Code reviews](#code-reviews)
   * [Code Style](#code-style)
+  * [TypeScript guidelines](#typescript-guidelines)
   * [API guidelines](#api-guidelines)
   * [Commit Messages](#commit-messages)
   * [Writing Documentation](#writing-documentation)
diff --git a/utils/doclint/check_public_api/JSBuilder.js b/utils/doclint/check_public_api/JSBuilder.js
index acf6d983..93d2ac57 100644
--- a/utils/doclint/check_public_api/JSBuilder.js
+++ b/utils/doclint/check_public_api/JSBuilder.js
@@ -189,7 +189,7 @@ function checkSources(sources) {
    * @return {boolean}
    */
   function symbolHasPrivateModifier(symbol) {
-    const modifiers = symbol.valueDeclaration.modifiers || [];
+    const modifiers = symbol.valueDeclaration && symbol.valueDeclaration.modifiers || [];
     return modifiers.some(modifier => modifier.kind === ts.SyntaxKind.PrivateKeyword);
   }