diff --git a/lib/test.js b/lib/test.js
index 18636c9..d5bbc80 100644
--- a/lib/test.js
+++ b/lib/test.js
@@ -7,6 +7,7 @@ var co = require('co-with-promise');
 var observableToPromise = require('observable-to-promise');
 var isPromise = require('is-promise');
 var isObservable = require('is-observable');
+var inspect = require('util').inspect;
 var assert = require('./assert');
 var enhanceAssert = require('./enhance-assert');
 var globals = require('./globals');
@@ -70,10 +71,6 @@ Test.prototype._setAssertError = function (err) {
 		return;
 	}
 
-	if (err === undefined) {
-		err = 'undefined';
-	}
-
 	this.assertError = err;
 };
 
@@ -95,7 +92,15 @@ Test.prototype._run = function () {
 	try {
 		ret = this.fn(this._publicApi());
 	} catch (err) {
-		this._setAssertError(err);
+		if (err instanceof Error) {
+			this._setAssertError(err);
+		} else {
+			this._setAssertError(new assert.AssertionError({
+				actual: err,
+				message: 'Non-error thrown with value: ' + inspect(err, {depth: null}),
+				operator: 'catch'
+			}));
+		}
 	}
 
 	return ret;
diff --git a/test/test.js b/test/test.js
index 194433b..109daed 100644
--- a/test/test.js
+++ b/test/test.js
@@ -356,17 +356,24 @@ test('fails with thrown falsy value', function (t) {
 	}).run();
 
 	t.is(result.passed, false);
-	t.is(result.reason, 0);
+	t.is(result.reason.actual, 0);
+	t.is(result.reason.message, 'Non-error thrown with value: 0');
+	t.is(result.reason.name, 'AssertionError');
+	t.is(result.reason.operator, 'catch');
 	t.end();
 });
 
-test('throwing undefined will be converted to string "undefined"', function (t) {
+test('fails with thrown non-error object', function (t) {
+	var obj = {foo: 'bar'};
 	var result = ava(function () {
-		throw undefined; // eslint-disable-line no-throw-literal
+		throw obj;
 	}).run();
 
 	t.is(result.passed, false);
-	t.is(result.reason, 'undefined');
+	t.is(result.reason.actual, obj);
+	t.is(result.reason.message, 'Non-error thrown with value: { foo: \'bar\' }');
+	t.is(result.reason.name, 'AssertionError');
+	t.is(result.reason.operator, 'catch');
 	t.end();
 });