C++ compatibility

diff --git a/skeletons/PrintableString.c b/skeletons/PrintableString.c
index 8589bd2..5c9a1fb 100644
--- a/skeletons/PrintableString.c
+++ b/skeletons/PrintableString.c
@@ -52,7 +52,7 @@
 int
 PrintableString_constraint(asn1_TYPE_descriptor_t *td, const void *sptr,
 		asn_app_consume_bytes_f *app_errlog, void *app_key) {
-	const PrintableString_t *st = sptr;
+	const PrintableString_t *st = (const PrintableString_t *)sptr;
 
 	if(st && st->buf) {
 		uint8_t *buf = st->buf;