How to track down Uglify error with Ember CLI

When I build my Ember CLI app in development, it works fine. When I try to build it for production, Uglify gets upset:

$ ember build --environment=production
version: 1.13.15
Build failed.
File: assets/vendor.js (70503:3)
Unexpected token name «use», expected punc «,»
Error
    at new JS_Parse_Error (eval at <anonymous> (/Users/michael/Code/queue/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:24:4), <anonymous>:1508:18)
    at js_error (eval at <anonymous> (/Users/michael/Code/queue/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:24:4), <anonymous>:1516:11)
    at croak (eval at <anonymous> (/Users/michael/Code/queue/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:24:4), <anonymous>:2008:9)
    at token_error (eval at <anonymous> (/Users/michael/Code/queue/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:24:4), <anonymous>:2016:9)
    at expect_token (eval at <anonymous> (/Users/michael/Code/queue/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:24:4), <anonymous>:2029:9)
    at expect (eval at <anonymous> (/Users/michael/Code/queue/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:24:4), <anonymous>:2032:36)
    at expr_list (eval at <anonymous> (/Users/michael/Code/queue/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:24:4), <anonymous>:2535:44)
    at subscripts (eval at <anonymous> (/Users/michael/Code/queue/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:24:4), <anonymous>:2674:30)
    at subscripts (eval at <anonymous> (/Users/michael/Code/queue/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:24:4), <anonymous>:2651:20)
    at expr_atom (eval at <anonymous> (/Users/michael/Code/queue/node_modules/broccoli-uglify-sourcemap/node_modules/uglify-js/tools/node.js:24:4), <anonymous>:2527:20)

I'm at a loss for what this error means - Unexpected token name «use», expected punc «,» - and assets/vendor.js (70503:3) isn't a file I can find anywhere.

If anybody can give me a suggestion of how to track down this error, I'd be really grateful!