diff --git a/calculator/calculator.app.js b/calculator/calculator.app.js
index 2622016..279fcc4 100644
--- a/calculator/calculator.app.js
+++ b/calculator/calculator.app.js
@@ -537,7 +537,7 @@ function buttonPress(val) {
       hasPressedNumber = false;
       break;
     case 'N':
-      if (results != null) {
+      if (results != null && !hasPressedNumber) {
         displayOutput(results *= -1);
         prevExpression = "-(" + prevExpression + ")";
       } else {