diff --git a/src/libsodium/crypto_core/ed25519/ref10/ed25519_ref10.c b/src/libsodium/crypto_core/ed25519/ref10/ed25519_ref10.c
index c4092b1f..9fe48b39 100644
--- a/src/libsodium/crypto_core/ed25519/ref10/ed25519_ref10.c
+++ b/src/libsodium/crypto_core/ed25519/ref10/ed25519_ref10.c
@@ -116,6 +116,10 @@ fe25519_invert(fe25519 out, const fe25519 z)
     fe25519_mul(out, t1, t0);
 }
 
+/*
+ * returns z^((p-5)/8) = z^(2^252-3)
+ * used to compute square roots since we have p=5 (mod 8); see Cohen and Frey.
+ */
 static void
 fe25519_pow22523(fe25519 out, const fe25519 z)
 {