diff --git a/armsrc/appmain.c b/armsrc/appmain.c
index 3b6976819..35838ffab 100644
--- a/armsrc/appmain.c
+++ b/armsrc/appmain.c
@@ -1591,7 +1591,7 @@ static void PacketReceived(PacketCommandNG *packet) {
             uint16_t offset = MIN(BIGBUF_SIZE - PM3_CMD_DATA_SIZE - 3, payload->offset);
 
             uint8_t *mem = BigBuf_get_addr();
-            memcpy(mem + offset, &payload->data, PM3_CMD_DATA_SIZE - 3);
+            memcpy(mem + offset, &payload->data, PM3_CMD_DATA_SIZE - 3 - offset);
             reply_ng(CMD_LF_UPLOAD_SIM_SAMPLES, PM3_SUCCESS, NULL, 0);
             break;
         }