diff --git a/src/apps/fido_u2f/__init__.py b/src/apps/fido_u2f/__init__.py
index e2e1d6a4..e4e30481 100644
--- a/src/apps/fido_u2f/__init__.py
+++ b/src/apps/fido_u2f/__init__.py
@@ -191,6 +191,8 @@ def read_cmd(iface: int) -> Cmd:
         databuf = bytearray(bcnt)
         utils.memcpy(databuf, 0, data, 0, bcnt)
         data = databuf
+    else:
+        data = data[:bcnt]
 
     while datalen < bcnt:
         buf, = yield loop.select(iface)
@@ -198,6 +200,11 @@ def read_cmd(iface: int) -> Cmd:
 
         cfrm = overlay_struct(buf, desc_cont)
 
+        if cfrm.seq == _CMD_INIT:
+            ifrm = overlay_struct(buf, desc_init)
+            data = ifrm.data[:ifrm.bcnt]
+            break
+
         if cfrm.cid != cid:
             send_cmd(cmd_error(cfrm.cid, _ERR_CHANNEL_BUSY), iface)
             continue