CSON with wrong indentation

report.txt

> CSON.parse('a: 2\n  b: 3\n c: 4')
Error: Syntax error on line 3: indentation is ambiguous
1 : a: 2
2 :   b: 3
3 :  c: 4
^ :~~^
    at Preprocessor.Preprocessor.consumeIndentation (/Users/jankrems/Projects/itier/libs/cson-safe/node_modules/coffee-script-redux/lib/preprocessor.js:155:17)
    at Preprocessor.Preprocessor.process (/Users/jankrems/Projects/itier/libs/cson-safe/node_modules/coffee-script-redux/lib/preprocessor.js:190:14)
    at Function.Preprocessor.Preprocessor.process (/Users/jankrems/Projects/itier/libs/cson-safe/node_modules/coffee-script-redux/lib/preprocessor.js:22:38)
    at Object.CoffeeScript.parse (/Users/jankrems/Projects/itier/libs/cson-safe/node_modules/coffee-script-redux/lib/module.js:47:35)
    at Object.parse (/Users/jankrems/Projects/itier/libs/cson-safe/lib/cson-safe.js:216:21)
    at repl:1:7
    at REPLServer.self.eval (repl.js:110:21)
    at Interface.<anonymous> (repl.js:239:12)
    at Interface.EventEmitter.emit (events.js:95:17)
    at Interface._onLine (readline.js:202:10)