diff --git a/microdroid/system/private/microdroid_manager.te b/microdroid/system/private/microdroid_manager.te
index 75c89be..96a05f7 100644
--- a/microdroid/system/private/microdroid_manager.te
+++ b/microdroid/system/private/microdroid_manager.te
@@ -129,7 +129,8 @@
 allow microdroid_manager ram_device:blk_file rw_file_perms;
 
 # Allow microdroid_manager to read/write failure serial device
-allow microdroid_manager serial_device:chr_file w_file_perms;
+# tcdrain requires ioctl.
+allow microdroid_manager serial_device:chr_file { w_file_perms ioctl };
 
 # Allow microdroid_manager to handle extra_apks
 allow microdroid_manager extra_apk_file:dir create_dir_perms;