diff --git a/src/PrimeToolKit.java b/src/PrimeToolKit.java
index dc543dc..2a92dad 100644
--- a/src/PrimeToolKit.java
+++ b/src/PrimeToolKit.java
@@ -5,7 +5,12 @@ public class PrimeToolKit {
 
   // From exercise 003
   static boolean isPrime(long number) {
-    return number > 1 && range(2, Math.round(Math.sqrt(number))).noneMatch(i -> number % i == 0);
+    if (number <= 1) return false;
+    long limit = Math.round(Math.sqrt(number));
+    for (long i = 2; i <= limit; i++) {
+      if (number % i == 0) return false;
+    }
+    return true;
   }
 
   // From exercise 007