diff --git a/crypto/pem/pvkfmt.c b/crypto/pem/pvkfmt.c
index 416bfc2a47e54615d2e3f01cc6a4055ce3efe220..248704ec594818c683c0e562ddf58c05a4a743d6 100644
--- a/crypto/pem/pvkfmt.c
+++ b/crypto/pem/pvkfmt.c
@@ -548,7 +548,7 @@ static void write_rsa(unsigned char **out, RSA *rsa, int ispub)
     hnbyte = (RSA_bits(rsa) + 15) >> 4;
     RSA_get0_key(rsa, &n, &e, &d);
     write_lebn(out, e, 4);
-    write_lebn(out, n, -1);
+    write_lebn(out, n, nbyte);
     if (ispub)
         return;
     RSA_get0_factors(rsa, &p, &q);