diff --git a/index.js b/index.js
index 6e9dcaf..acca685 100644
--- a/index.js
+++ b/index.js
@@ -3,6 +3,10 @@
 
 var index = require('./package.json');
 
+function isFunction(functionToCheck) {
+	return typeof functionToCheck === 'function';
+}
+
 if(global[index.name] && global[index.name].version === index.version) {
 	module.exports = global[index.name];
 } else {
@@ -18,16 +22,14 @@ if(global[index.name] && global[index.name].version === index.version) {
 	//detector.find = detection.find;
 	detector.find = function(vid, pid, callback) {
 		// Suss out the optional parameters
-		if(!pid && !callback) {
+		if(isFunction(vid) && !pid && !callback) {
 			callback = vid;
 			vid = undefined;
-		}
-		else if(!callback) {
+		} else if(isFunction(pid) && !callback) {
 			callback = pid;
 			pid = undefined;
 		}
 
-
 		return new Promise(function(resolve, reject) {
 			// Assemble the optional args into something we can use with `apply`
 			var args = [];
diff --git a/test/test.js b/test/test.js
index 8a1ad6d..faf45f3 100644
--- a/test/test.js
+++ b/test/test.js
@@ -63,6 +63,33 @@ describe('usb-detection', function() {
 				});
 			});
 
+			it('should return a promise when vid and pid are given', async function(done) {
+				const devices = await usbDetect.find();
+				usbDetect.find(devices[0].vendorId, devices[0].productId)
+					.then(function(devicesFromTestedFunction) {
+						testArrayOfDevicesShape(devicesFromTestedFunction);
+						expect(devicesFromTestedFunction.length).to.be.greaterThan(0);
+						// Should find a subset of USB devices. We assume you have many USB devices connected
+						expect(devicesFromTestedFunction.length).to.be.lessThan(devices.length);
+					})
+					.then(done)
+					.catch(done.fail);
+			});
+
+			it('should return a promise when vid is given', async function(done) {
+				const devices = await usbDetect.find();
+				usbDetect.find(devices[0].vendorId)
+					.then(function(devicesFromTestedFunction) {
+						testArrayOfDevicesShape(devicesFromTestedFunction);
+						expect(devicesFromTestedFunction.length).to.be.greaterThan(0);
+						// Should find a subset of USB devices. We assume you have many USB devices connected
+						expect(devicesFromTestedFunction.length).to.be.lessThan(devices.length);
+					})
+					.then(done)
+					.catch(done.fail);
+			});
+
+
 			it('should return a promise', function(done) {
 				usbDetect.find()
 					.then(function(devices) {