Index: asn1-x509.c
==================================================================
--- asn1-x509.c
+++ asn1-x509.c
@@ -209,11 +209,11 @@
 	struct x509_object x509;
 	int read_ret;
 
 	read_ret = asn1_x509_read_object(x509_der_buf, x509_der_buf_len, &x509);
 	if (read_ret != 0) {
-		CACKEY_DEBUG_PRINTF("Unable to read serial number from a %lu byte buffer", x509_der_buf_len);
+		CACKEY_DEBUG_PRINTF("Unable to read serial number from a %lu byte buffer", (unsigned long) x509_der_buf_len);
 		CACKEY_DEBUG_PRINTBUF("X.509 DER:", x509_der_buf, x509_der_buf_len);
 
 		return(-1);
 	}