diff --git a/src/pki_mbedcrypto.c b/src/pki_mbedcrypto.c
index fceacd80..534e375d 100644
--- a/src/pki_mbedcrypto.c
+++ b/src/pki_mbedcrypto.c
@@ -1046,7 +1046,7 @@ static ssh_string rsa_do_sign_hash(const unsigned char *digest,
     }
 
     ssh_string_fill(sig_blob, sig, slen);
-    memset(sig, 'd', slen);
+    explicit_bzero(sig, slen);
     SAFE_FREE(sig);
 
     return sig_blob;