Fix warning.
diff --git a/apps/x509.c b/apps/x509.c
index 3229a2c..2972b04 100644
--- a/apps/x509.c
+++ b/apps/x509.c
@@ -1032,7 +1032,7 @@
 	MS_STATIC char buf2[1024];
 	ASN1_INTEGER *bs = NULL, bs2;
 	BIO *io = NULL;
-	BIGNUM *serial;
+	BIGNUM *serial = NULL;
 	buf=OPENSSL_malloc( ((serialfile == NULL)
 			?(strlen(CAfile)+strlen(POSTFIX)+1)
 			:(strlen(serialfile)))+1);