diff --git a/artiq/coredevice/gpio.py b/artiq/coredevice/gpio.py
index 9477da861..aaa8ea212 100644
--- a/artiq/coredevice/gpio.py
+++ b/artiq/coredevice/gpio.py
@@ -4,7 +4,7 @@ from artiq.language.db import *
 
 class GPIOOut(AutoDB):
     class DBKeys:
-    	core = Device()
+        core = Device()
         channel = Argument()
 
     @kernel