diff --git a/du3/program.c b/du3/program.c
index 3a65bc4..d07ebe8 100644
--- a/du3/program.c
+++ b/du3/program.c
@@ -12,6 +12,8 @@
 float IsArithCorrect(float num1, float num2, char op, float result)
 {
     float calcResult = 0;
+    
+    if (num1 == '/' && num2 == 0) { return -1;}
 
     switch (op)
     {