diff --git a/perftune/sieve.c b/perftune/sieve.c
index f7cfdb3a0a2728ce4c11e3bdd9bb7d09321150e2..34112e25e111941e0f6f530ef228e316d6044772 100644
--- a/perftune/sieve.c
+++ b/perftune/sieve.c
@@ -18,7 +18,7 @@ int *sieve(int n) {
     is_prime[j] = false;
 
   for (int i = 3; i <= n; i+=2) {
-    if(!is_prime[i]) continue;  //use prime only
+    if(is_prime[i]) continue;  //use prime only
     for (int j = i + i + i; j <= n; j += (i+i)) {
       is_prime[j] = false;
     }