diff --git a/is_prime b/is_prime
index 482288a..5f1650e 100644
--- a/is_prime
+++ b/is_prime
@@ -1,4 +1,4 @@
-long 967938954523L
+long a = 967938954523L; // for Windows it has to be unsigned long long
 
 unsigned long long i = 18446744073709551557L;