diff --git a/api/controller.js b/api/controller.js
index 949731c..f3a8f20 100644
--- a/api/controller.js
+++ b/api/controller.js
@@ -42,3 +42,10 @@ exports.calculate = function(req, res) {
 
   res.json({ result: operation(req.query.operand1, req.query.operand2) });
 };
+
+//Make a change
+  if (!req.query.operand2 ||
+      !req.query.operand2.match(/^(-)?[0-9\.]+(e(-)?[0-9]+)?$/) ||
+      req.query.operand2.replace(/[-0-9e]/g, '').length > 1) {
+    throw new Error("Invalid operand2: " + req.query.operand2);
+  }