diff --git a/sha3/sha3_test.go b/sha3/sha3_test.go
index cbf811d..caf72f2 100644
--- a/sha3/sha3_test.go
+++ b/sha3/sha3_test.go
@@ -159,7 +159,7 @@ func TestAppend(t *testing.T) {
 	testUnalignedAndGeneric(t, func(impl string) {
 		d := New224()
 
-		for capacity := 2; capacity < 64; capacity += 64 {
+		for capacity := 2; capacity <= 66; capacity += 64 {
 			// The first time around the loop, Sum will have to reallocate.
 			// The second time, it will not.
 			buf := make([]byte, 2, capacity)