diff --git a/src/libsodium/crypto_sign/ed25519/ref10/open.c b/src/libsodium/crypto_sign/ed25519/ref10/open.c
index 95319950..38c48ee0 100644
--- a/src/libsodium/crypto_sign/ed25519/ref10/open.c
+++ b/src/libsodium/crypto_sign/ed25519/ref10/open.c
@@ -28,7 +28,7 @@ crypto_sign_check_S_lt_l(const unsigned char *S)
         n &= ((S[i] ^ l[i]) - 1) >> 8;
     } while (i != 0);
 
-    return -(c == 0);
+    return ((int) c) - 1;
 }
 #endif