diff --git a/lib/build/slim.js b/lib/build/slim.js
index fe4e0944..9dc7ba0f 100644
--- a/lib/build/slim.js
+++ b/lib/build/slim.js
@@ -27,24 +27,26 @@ var write = require("../bundle/write_bundles").createWriteStream;
 var writeBundlesManifest = require("../stream/write_bundle_manifest");
 var graph = require("../graph/make_graph_with_bundles").createBundleGraphStream;
 
-module.exports = function(config, options) {
+module.exports = function(cfg, opts) {
+	var config = cfg !== undefined ? cfg : {};
+	var options = opts !== undefined ? opts : {};
+
 	var slimDfd = makeDeferred();
-	var buildOptions = assign({}, options);
 	var supportedTargets = ["web", "node", "worker"];
 
 	// minification is on by default
-	assign(buildOptions, {
-		minify: isUndefined(buildOptions.minify) ? true : buildOptions.minify
+	assign(options, {
+		minify: isUndefined(options.minify) ? true : options.minify
 	});
 
 	try {
-		options = assignDefaultOptions(config, buildOptions);
+		options = assignDefaultOptions(config, options);
 	} catch (err) {
 		return Promise.reject(err);
 	}
 
 	// fail early if an unknown target is passed in
-	var targets = arrify(buildOptions.target);
+	var targets = arrify(options.target);
 	if (difference(targets, supportedTargets).length) {
 		var unknown = difference(targets, supportedTargets);
 		return Promise.reject(
@@ -55,7 +57,7 @@ module.exports = function(config, options) {
 	}
 
 	var initialStream = pump(
-		graph(config, buildOptions),
+		graph(config, options),
         buildType("optimize"),
 		filterGraph(),
 		checkSlimSupport(),
diff --git a/test/slim_build_test.js b/test/slim_build_test.js
index 2a6c1754..b4490c83 100644
--- a/test/slim_build_test.js
+++ b/test/slim_build_test.js
@@ -378,6 +378,7 @@ describe("slim builds", function() {
 			});
 	});
 
+
 	it("rejects build promise if unknown target passed in", function(done) {
 		var base = path.join(__dirname, "slim", "basics");
 		var config = { config: path.join(base, "stealconfig.js") };
@@ -392,6 +393,23 @@ describe("slim builds", function() {
 			});
 	});
 
+	it("config argument is optional", function(done) {
+		// passing options to force the rejection due to unknown target
+		optimize(undefined, { quiet: true, target: "electron" })
+			.then(
+				function() {
+					done(new Error("build promise should not resolve"));
+				},
+				function(error) {
+					assert(
+						/Cannot create slim build/.test(error.message),
+						"Incorrect error message: " + error.message
+					);
+					done();
+			})
+			.catch(done);
+	});
+
 	it("writes targets in folders matching the target name", function() {
 		var base = path.join(__dirname, "slim", "basics");
 		var config = { config: path.join(base, "stealconfig.js") };