diff --git a/index.js b/index.js
index 636af8d..96ad4c6 100644
--- a/index.js
+++ b/index.js
@@ -1,5 +1,7 @@
 exports.fibonacci = function(n) {
     if(n==0 || n==1)
         return n;
+    if (n<0)
+        return (undefined);
     return this.fibonacci(n-1) + this.fibonacci(n-2);
 }
\ No newline at end of file
diff --git a/test/test.js b/test/test.js
index 0160835..e9f4b05 100644
--- a/test/test.js
+++ b/test/test.js
@@ -6,6 +6,12 @@ describe('Regular fibonacci value', function() {
       });
 });
 
+describe('negative fibonacci value', function() {
+  it('should return undefined for fib(-3)', function() {
+      assert.strictEqual(main.fibonacci(-3), undefined);
+  });
+});
+
 describe('First two terms', function() {
   it('should return 0 and 1 for first two terms', function() {
       assert.strictEqual(main.fibonacci(0), 0);