diff --git a/libnfc/chips/pn53x.c b/libnfc/chips/pn53x.c
index 157cbd7..807504f 100644
--- a/libnfc/chips/pn53x.c
+++ b/libnfc/chips/pn53x.c
@@ -1206,7 +1206,7 @@ pn53x_initiator_poll_target(struct nfc_device *pnd,
   if (CHIP_DATA(pnd)->type == PN532) {
     size_t szTargetTypes = 0;
     pn53x_target_type apttTargetTypes[32];
-    memset(apttTargetTypes, PTT_UNDEFINED, 32);
+    memset(apttTargetTypes, PTT_UNDEFINED, 32 * sizeof(pn53x_target_type));
     for (size_t n = 0; n < szModulations; n++) {
       const pn53x_target_type ptt = pn53x_nm_to_ptt(pnmModulations[n]);
       if (PTT_UNDEFINED == ptt) {