diff --git a/Chapter_4/ex1.py b/Chapter_4/ex1.py
index 8b5ac2148a1cdccf21ebde115ef177637dbf26a8..757b85db580e596c8a7d3d5cbe3f457a2f42871b 100644
--- a/Chapter_4/ex1.py
+++ b/Chapter_4/ex1.py
@@ -15,7 +15,7 @@ def is_prime(number):
     if number == 2:
         return True
 
-    for test in range(2,int(math.sqrt(number))):
+    for test in range(2,int(math.sqrt(number))+1):
         if (number % test) == 0:
             return False
     return True