diff --git a/Boolean-Algebra/script.js b/Boolean-Algebra/script.js
index 1af22fb..969379c 100644
--- a/Boolean-Algebra/script.js
+++ b/Boolean-Algebra/script.js
@@ -66,6 +66,7 @@ function Evaluate() {
     let formulaValuesRPNArray = ConvertCharsToValues(formulaRPNArray);
 
     let result = SolveRPNFormula(formulaValuesRPNArray);
+    if (result == undefined) return;
     let readableResult = ConvertToReadableResult(result);
 
     let resultField = document.getElementById('result');
@@ -272,6 +273,7 @@ function StepByStep() {
     let formulaValuesRPNArray = ConvertCharsToValues(formulaRPNArray);
 
     let result = SolveRPNFormula(formulaValuesRPNArray);
+    if (result == undefined) return;
     let readableResult = ConvertToReadableResult(result);
 
     let resultField = document.getElementById('result');