diff --git a/tools/mpremote/mpremote/transport_serial.py b/tools/mpremote/mpremote/transport_serial.py
index 23a379d16b488..e212973be4111 100644
--- a/tools/mpremote/mpremote/transport_serial.py
+++ b/tools/mpremote/mpremote/transport_serial.py
@@ -753,7 +753,12 @@ def ioctl(self, request, arg):
             machine.mem32[arg] = self.seek(machine.mem32[arg], machine.mem32[arg + 4])
         elif request == 4:  # CLOSE
             self.close()
-        return 0
+        elif request == 11:  # BUFFER_SIZE
+            # This is used as the vfs_reader buffer. n + 4  should be less than 255 to
+            # fit in stdin ringbuffer on supported ports. n + 7 should be multiple of 16
+            # to efficiently use gc blocks in mp_reader_vfs_t.
+            return 249
+        return -1
 
     def flush(self):
         pass