diff --git a/src/libsodium/crypto_core/ed25519/ref10/ed25519_ref10.c b/src/libsodium/crypto_core/ed25519/ref10/ed25519_ref10.c
index a775c37a..0e743590 100644
--- a/src/libsodium/crypto_core/ed25519/ref10/ed25519_ref10.c
+++ b/src/libsodium/crypto_core/ed25519/ref10/ed25519_ref10.c
@@ -2498,6 +2498,7 @@ sc25519_is_canonical(const unsigned char s[32])
     return (c != 0);
 }
 
+/* x^((p-1)/2) */
 static void
 chi25519(fe25519 out, const fe25519 z)
 {