diff --git a/library/ecdsa.c b/library/ecdsa.c
index dc169ce..3484a74 100644
--- a/library/ecdsa.c
+++ b/library/ecdsa.c
@@ -220,8 +220,8 @@
                            void *p_rng )
 {
     int ret;
-    unsigned char buf[MAX_SIG_LEN + 3];
-    unsigned char *p = buf + MAX_SIG_LEN;
+    unsigned char buf[MAX_SIG_LEN];
+    unsigned char *p = buf + sizeof( buf );
     size_t len = 0;
 
     if( ( ret = ecdsa_sign( &ctx->grp, &ctx->r, &ctx->s, &ctx->d,