diff --git a/.travis.yml b/.travis.yml
index 31d07777..f7059a13 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,6 +5,8 @@ before_install:
   - curl -o factorio.tar.gz -L https://www.factorio.com/get-download/latest/headless/linux64
   - tar -xf factorio.tar.gz
   - npm install -g codecov
+  # Needed for lib/manager/configManager
+  - echo {} > config.json
 script:
   - npm run-script ci-cover
   - codecov -f coverage/lcov.info
diff --git a/CHANGELOG.md b/CHANGELOG.md
index a0dfdd58..64085b0a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ Version 2.0.0
 - Fixed sslCert and sslPrivKey entries being ignored in the config.
 - Changed ssl key creation to be done at startup instead of on npm install.
 - Added error handling during master startup.
+- Factorio game and rcon port now defaults to a random port above 49151.
 
 ### Breaking Changes
 
diff --git a/client.js b/client.js
index 53d22417..d237a28c 100644
--- a/client.js
+++ b/client.js
@@ -90,6 +90,21 @@ function messageInterface(command, callback) {
 	});
 }
 
+/**
+ * Give a random dynamic port
+ *
+ * Returns a random port number in the Dynamic Ports range as defined by
+ * RFC 6335.
+ *
+ * @return {number} a number in the range 49152 to 65535.
+ */
+function randomDynamicPort() {
+	const start = 49152;
+	const end = 65535 + 1;
+
+	return Math.floor(Math.random() * (end - start) + start)
+}
+
 function printUsage() {
 	console.error("Usage: ");
 	console.error("node client.js start [instance name]");
@@ -264,8 +279,8 @@ write-data=${ path.resolve(config.instanceDirectory, instance) }\r\n
 	// this line is probably not needed anymore but Im not gonna remove it
 	fs.copySync('sharedMods', path.join(instancedirectory, "mods"));
 	let instconf = {
-		"factorioPort": args.port || process.env.FACTORIOPORT || Math.floor(Math.random() * 65535),
-		"clientPort": args["rcon-port"] || process.env.RCONPORT || Math.floor(Math.random() * 65535),
+		"factorioPort": args.port || process.env.FACTORIOPORT || randomDynamicPort(),
+		"clientPort": args["rcon-port"] || process.env.RCONPORT || randomDynamicPort(),
 		"__comment_clientPassword": "This is the rcon password. Its also used for making an instanceID. Make sure its unique and not blank.",
 		"clientPassword": args["rcon-password"] || Math.random().toString(36).replace(/[^a-z]+/g, '').substr(0, 8),
 		"info": {}
@@ -802,6 +817,11 @@ function hashMods(instanceName, callback) {
 	});
 }
 
+module.exports = {
+
+	// For testing only
+	_randomDynamicPort: randomDynamicPort,
+};
 
 if (module === require.main) {
 	console.warn(`
diff --git a/client.spec.js b/client.spec.js
new file mode 100644
index 00000000..5fd9e9ff
--- /dev/null
+++ b/client.spec.js
@@ -0,0 +1,23 @@
+const assert = require('assert').strict;
+
+const client = require("./client");
+
+describe("Client testing", function() {
+	describe("randomDynamicPort()", function() {
+		it("should return a port number", function() {
+			let port = client._randomDynamicPort()
+			assert.equal(typeof port, "number");
+			assert(Number.isInteger(port));
+			assert(0 <= port && port < 2**16);
+		});
+
+		it("should return a port number in the dynamic range", function() {
+			function validate(port) {
+				return 49152 <= port && port <= 65535;
+			}
+			for (let i=0; i < 20; i++) {
+				assert(validate(client._randomDynamicPort()));
+			}
+		});
+	});
+});