diff --git a/client/comms.c b/client/comms.c
index b08345db3..4840a6b4a 100644
--- a/client/comms.c
+++ b/client/comms.c
@@ -173,7 +173,7 @@ void SendCommandNG(uint16_t cmd, uint8_t *data, size_t len) {
 
 void SendCommandMIX(uint64_t cmd, uint64_t arg0, uint64_t arg1, uint64_t arg2, void *data, size_t len) {
     uint64_t arg[3] = {arg0, arg1, arg2};
-    if (len > USB_CMD_DATA_SIZE - sizeof(arg)) {
+    if (len > USB_CMD_DATA_SIZE_MIX) {
         PrintAndLogEx(WARNING, "Sending %d bytes of payload is too much for MIX frames, abort", len);
         return;
     }
diff --git a/include/usb_cmd.h b/include/usb_cmd.h
index 75ceb8515..f40a71dbc 100644
--- a/include/usb_cmd.h
+++ b/include/usb_cmd.h
@@ -28,6 +28,7 @@ typedef BYTE uint8_t;
 #endif
 
 #define USB_CMD_DATA_SIZE 512
+#define USB_CMD_DATA_SIZE_MIX ( USB_CMD_DATA_SIZE - 3 * sizeof(uint64_t) )
 
 typedef struct {
     uint64_t cmd;