diff --git a/eratosthenes_parallel.go b/eratosthenes_parallel.go
index 517e34a..0489826 100644
--- a/eratosthenes_parallel.go
+++ b/eratosthenes_parallel.go
@@ -36,8 +36,16 @@ func main() {
 
 			p := nCpus
 			var jnext int64
+			// XXX - i * i can overflow.
+			// bail out before that happens
+			if n / i < i {
+				continue;
+			}
 			for j := i * i; j < n; j = jnext {
 				jnext = ((n-j)/(2*i)/p+1)*(2*i) + j
+				if jnext > n {
+					jnext = n
+				}
 				markGroup.Add(1)
 				go markMultiples(sieve, i, j, jnext)
 				p--