diff --git a/packages/babel-plugin-transform-es2015-instanceof/src/index.js b/packages/babel-plugin-transform-es2015-instanceof/src/index.js
index e2ac29e304..9eaa2e7a23 100644
--- a/packages/babel-plugin-transform-es2015-instanceof/src/index.js
+++ b/packages/babel-plugin-transform-es2015-instanceof/src/index.js
@@ -9,6 +9,7 @@ export default function({ types: t }) {
             return (
               (path.isVariableDeclarator() && path.node.id === helper) ||
               (path.isFunctionDeclaration() &&
+                path.node.id &&
                 path.node.id.name === helper.name)
             );
           });