diff --git a/src/lib.rs b/src/lib.rs
index 4bc7738..0374581 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -27,7 +27,7 @@ fn block_bit(x: &u64, d: &u64) -> (u64, u64) {
     (x / d, x % d)
 }
 
-#[derive(PartialEq)]
+#[derive(PartialEq, Eq)]
 pub struct BitSet {
     blocks: Storage,
     nbits: usize,