diff --git a/ports/esp32/modules/inisetup.py b/ports/esp32/modules/inisetup.py
index 00d9a4eab8..3196f0c6f3 100644
--- a/ports/esp32/modules/inisetup.py
+++ b/ports/esp32/modules/inisetup.py
@@ -2,7 +2,7 @@ import uos
 from flashbdev import bdev
 
 def check_bootsec():
-    buf = bytearray(bdev.SEC_SIZE)
+    buf = bytearray(bdev.ioctl(5, 0)) # 5 is SEC_SIZE
     bdev.readblocks(0, buf)
     empty = True
     for b in buf: