diff --git a/.travis.yml b/.travis.yml
index ed4c1ca..d5cb0ac 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,7 +2,11 @@ language: node_js
 node_js:
 - 6
 - 8
+- 9
 
 before_install:
 - sudo apt-get -qq update
 - sudo apt-get install -y realpath
+
+script:
+- npm test
diff --git a/lib/manager.js b/lib/manager.js
index ee447c7..59c5e90 100644
--- a/lib/manager.js
+++ b/lib/manager.js
@@ -91,7 +91,7 @@ function resolveModulePath(filepath, rootDir) {
 	if(legacy) {
 		legacy = process.env.NODE_PATH; // cache previous value
 		rootDir = rootDir.replace(/\/{1,}$/, ""); // strip trailing slashes, to be safe
-		process.env.NODE_PATH = rootDir + "/node_modules";
+		process.env.NODE_PATH = `${rootDir}:${rootDir}/node_modules`;
 		require("module").Module._initPaths();
 	}
 
diff --git a/test/fixtures/dummy/index.js b/test/fixtures/dummy/index.js
new file mode 100644
index 0000000..5d36d63
--- /dev/null
+++ b/test/fixtures/dummy/index.js
@@ -0,0 +1 @@
+export default "SRC";
diff --git a/test/fixtures/dummy/src.js b/test/fixtures/dummy/src.js
new file mode 100644
index 0000000..5d36d63
--- /dev/null
+++ b/test/fixtures/dummy/src.js
@@ -0,0 +1 @@
+export default "SRC";
diff --git a/test/fixtures/node_modules/dummy/index.js b/test/fixtures/node_modules/dummy/index.js
new file mode 100644
index 0000000..7f3e7f0
--- /dev/null
+++ b/test/fixtures/node_modules/dummy/index.js
@@ -0,0 +1 @@
+void 0;
diff --git a/test/fixtures/node_modules/dummy/pkg.js b/test/fixtures/node_modules/dummy/pkg.js
new file mode 100644
index 0000000..7f3e7f0
--- /dev/null
+++ b/test/fixtures/node_modules/dummy/pkg.js
@@ -0,0 +1 @@
+void 0;
diff --git a/test/test_manager.js b/test/test_manager.js
new file mode 100644
index 0000000..49330d8
--- /dev/null
+++ b/test/test_manager.js
@@ -0,0 +1,39 @@
+/* global describe, before, after, it */
+"use strict";
+
+let AssetManager = require("../lib/manager");
+let path = require("path");
+let assert = require("assert");
+
+let assertSame = assert.strictEqual;
+
+describe("asset manager", _ => {
+	let cwd;
+
+	before(() => {
+		cwd = process.cwd();
+	});
+
+	after(() => {
+		process.chdir(cwd);
+	});
+
+	it("resolves file paths for local modules and third-party packages", () => {
+		let root = path.resolve(__dirname, "fixtures");
+		process.chdir(root);
+
+		let { resolvePath } = new AssetManager(root);
+
+		let filepath = resolvePath("dummy/src.js");
+		assertSame(path.relative(root, filepath), "dummy/src.js");
+
+		filepath = resolvePath("dummy/pkg.js");
+		assertSame(path.relative(root, filepath), "node_modules/dummy/pkg.js");
+
+		// local modules take precedence over third-party packages
+		["dummy", "dummy/index", "dummy/index.js"].forEach(module => {
+			let filepath = resolvePath(module);
+			assertSame(path.relative(root, filepath), "dummy/index.js");
+		});
+	});
+});