diff --git a/client/src/mifare/desfirecore.c b/client/src/mifare/desfirecore.c
index 5b32176b6..3ab153f78 100644
--- a/client/src/mifare/desfirecore.c
+++ b/client/src/mifare/desfirecore.c
@@ -694,6 +694,7 @@ static void DesfireJoinBlockToBytes(uint8_t *blockdata, size_t blockdatacount, s
 static void DesfireSplitBytesToBlock(uint8_t *blockdata, size_t *blockdatacount, size_t blockdatasize, uint8_t *dstdata, size_t dstdatalen) {
     size_t len = 0;
     for (int i = 0; i < *blockdatacount; i++) {
+        memset(&blockdata[i * blockdatasize + 1], 0, blockdatasize - 1);
         size_t tlen = len + blockdata[i * blockdatasize];
         if (tlen > dstdatalen) {
             tlen = dstdatalen;