diff --git a/solo.c b/solo.c
index 766adde..6987872 100644
--- a/solo.c
+++ b/solo.c
@@ -1473,7 +1473,7 @@ static int solver_killer_sums(struct solver_usage *usage, int b,
     }
     assert(nsquares > 0);
 
-    if (nsquares > 4)
+    if (nsquares < 2 || nsquares > 4)
 	return 0;
 
     if (!cage_is_region) {