diff --git a/crypto/bn256/google/optate.go b/crypto/bn256/google/optate.go
index 9d6957062e..3c32515a90 100644
--- a/crypto/bn256/google/optate.go
+++ b/crypto/bn256/google/optate.go
@@ -6,7 +6,7 @@ package bn256
 
 func lineFunctionAdd(r, p *twistPoint, q *curvePoint, r2 *gfP2, pool *bnPool) (a, b, c *gfP2, rOut *twistPoint) {
 	// See the mixed addition algorithm from "Faster Computation of the
-	// Tate Pairing", http://arxiv.org/pdf/0904.0854v3.pdf
+	// Tate Pairing", <https://arxiv.org/pdf/0904.0854v3.pdf>.
 
 	B := newGFp2(pool).Mul(p.x, r.t, pool)