diff --git a/packages/lib/file_ops.js b/packages/lib/file_ops.js
index 577734b4..bc5fe91e 100644
--- a/packages/lib/file_ops.js
+++ b/packages/lib/file_ops.js
@@ -32,6 +32,44 @@ async function getNewestFile(directory, filter = (name) => true) {
 	return newestFile;
 }
 
+/**
+ * Modifies name in case it already exisist at the given directory
+ *
+ * Checks the directory passed if it already contains a file or folder with
+ * the given name, if it does not returns name unmodified, otherwise it
+ * returns a modified name that does not exist in the directory.
+ *
+ * Warning: this function should not be relied upon to be accurate for
+ * security sensitive applications.  The selection process is inherently
+ * racy and a file or folder may have been created in the folder by the time
+ * this function returns.
+ *
+ * @param {string} directory - directory to check in.
+ * @param {string} name - file name to check for, may have extension.
+ * @param {string} extension - dot extension used for the file name.
+ * @returns {string} modified name with extension that likely does not exist
+ *     in the folder
+ */
+async function findUnusedName(directory, name, extension = "") {
+	if (extension && name.endsWith(extension)) {
+		name = name.slice(0, -extension.length);
+	}
+
+	while (true) {
+		if (!await fs.pathExists(path.join(directory, `${name}${extension}`))) {
+			return `${name}${extension}`;
+		}
+
+		let match = /^(.*?)(-(\d+))?$/.exec(name);
+		if (!match[2]) {
+			name = `${match[1]}-2`;
+		} else {
+			name = `${match[1]}-${Number.parseInt(match[3], 10) + 1}`;
+		}
+	}
+}
+
 module.exports = {
 	getNewestFile,
+	findUnusedName,
 };
diff --git a/packages/slave/slave.js b/packages/slave/slave.js
index b6dc2df9..3aacbff9 100755
--- a/packages/slave/slave.js
+++ b/packages/slave/slave.js
@@ -1102,13 +1102,8 @@ class Slave extends libLink.Link {
 			throw new Error(`Instance name ${err.message}`);
 		}
 
-		// For now add dashes until an unused directory name is found
-		let dir = path.join(this.config.get("slave.instances_directory"), name);
-		while (await fs.pathExists(dir)) {
-			dir += "-";
-		}
-
-		return dir;
+		let instancesDir = this.config.get("slave.instances_directory");
+		return path.join(instancesDir, await libFileOps.findUnusedName(instancesDir, name));
 	}
 
 	async forwardRequestToInstance(message, request) {
diff --git a/test/lib/file_ops.js b/test/lib/file_ops.js
index da153c92..5b02656d 100644
--- a/test/lib/file_ops.js
+++ b/test/lib/file_ops.js
@@ -13,6 +13,13 @@ describe("lib/file_ops", function() {
 
 		await fs.outputFile(path.join(baseDir, "test", "file.txt"), "contents");
 		await fs.outputFile(path.join(baseDir, "test", "another file.txt"), "more contents");
+
+		await fs.outputFile(path.join(baseDir, "find", "file"), "contents");
+		await fs.outputFile(path.join(baseDir, "find", "file.txt"), "contents");
+		await fs.outputFile(path.join(baseDir, "find", "foo-1"), "contents");
+		await fs.outputFile(path.join(baseDir, "find", "foo-2"), "contents");
+		await fs.outputFile(path.join(baseDir, "find", "bar-1.txt"), "contents");
+		await fs.outputFile(path.join(baseDir, "find", "bar-2.txt"), "contents");
 	}
 
 	before(setupTestingEnv);
@@ -31,4 +38,32 @@ describe("lib/file_ops", function() {
 			assert.equal(newest, null);
 		});
 	});
+
+	describe("findUnusedName()", function() {
+		it("should return named unchanged if it does not exist", async function() {
+			let cases = [
+				[["file"], "file"],
+				[["file", ".txt"], "file.txt"],
+				[["file.txt", ".txt"], "file.txt"],
+			];
+			for (let [args, expected] of cases) {
+				let actual = await libFileOps.findUnusedName(path.join(baseDir, "test", "folder"), ...args);
+				assert.equal(actual, expected);
+			}
+		});
+		it("should return changed name if it does exist", async function() {
+			let cases = [
+				[["file"], "file-2"],
+				[["file", ".txt"], "file-2.txt"],
+				[["file.txt", ".txt"], "file-2.txt"],
+				[["foo-1"], "foo-3"],
+				[["bar-1", ".txt"], "bar-3.txt"],
+				[["bar-1.txt", ".txt"], "bar-3.txt"],
+			];
+			for (let [args, expected] of cases) {
+				let actual = await libFileOps.findUnusedName(path.join(baseDir, "find"), ...args);
+				assert.equal(actual, expected);
+			}
+		});
+	});
 });