diff --git a/src/libopensc/opensc-pkcs15.h b/src/libopensc/opensc-pkcs15.h
index 571b5153..701d8a9a 100644
--- a/src/libopensc/opensc-pkcs15.h
+++ b/src/libopensc/opensc-pkcs15.h
@@ -101,11 +101,12 @@ struct sc_pkcs15_pubkey_rsa {
 
 struct sc_pkcs15_cert {
 	int version;
-	unsigned long serial;
+	u8 *serial;
+	size_t serial_len;
 
 	struct sc_pkcs15_pubkey_rsa key;
 	u8 *data;	/* DER encoded raw cert */
-	int data_len;
+	size_t data_len;
 };
 
 struct sc_pkcs15_cert_info {
diff --git a/src/libopensc/pkcs15-cert.c b/src/libopensc/pkcs15-cert.c
index dd9c12ff..41b69222 100644
--- a/src/libopensc/pkcs15-cert.c
+++ b/src/libopensc/pkcs15-cert.c
@@ -68,7 +68,7 @@ static int parse_x509_cert(struct sc_context *ctx, const u8 *buf, size_t buflen,
 	};
 	struct sc_asn1_entry asn1_tbscert[] = {
 		{ "version",		SC_ASN1_STRUCT,    SC_ASN1_CTX | 0 | SC_ASN1_CONS, 0, asn1_version },
-		{ "serialNumber",	SC_ASN1_INTEGER,   ASN1_INTEGER, 0, &cert->serial },
+		{ "serialNumber",	SC_ASN1_OCTET_STRING, ASN1_INTEGER, SC_ASN1_ALLOC, &cert->serial, &cert->serial_len },
 		{ "signature",		SC_ASN1_STRUCT,    ASN1_SEQUENCE | SC_ASN1_CONS, 0, NULL },
 		{ "issuer",		SC_ASN1_STRUCT,	   ASN1_SEQUENCE | SC_ASN1_CONS, 0, NULL },
 		{ "validity",		SC_ASN1_STRUCT,    ASN1_SEQUENCE | SC_ASN1_CONS, 0, NULL },
diff --git a/src/libopensc/pkcs15.h b/src/libopensc/pkcs15.h
index 571b5153..701d8a9a 100644
--- a/src/libopensc/pkcs15.h
+++ b/src/libopensc/pkcs15.h
@@ -101,11 +101,12 @@ struct sc_pkcs15_pubkey_rsa {
 
 struct sc_pkcs15_cert {
 	int version;
-	unsigned long serial;
+	u8 *serial;
+	size_t serial_len;
 
 	struct sc_pkcs15_pubkey_rsa key;
 	u8 *data;	/* DER encoded raw cert */
-	int data_len;
+	size_t data_len;
 };
 
 struct sc_pkcs15_cert_info {