diff --git a/artiq/gateware/ad9xxx.py b/artiq/gateware/ad9xxx.py
index 439ece554b..0bd290df73 100644
--- a/artiq/gateware/ad9xxx.py
+++ b/artiq/gateware/ad9xxx.py
@@ -55,7 +55,11 @@ def __init__(self, pads,
             dts.oe.eq(~rx)
         ]
 
-        gpio = Signal(flen(pads.sel) + 1)
+        if hasattr(pads, "sel"):
+            sel_len = flen(pads.sel)
+        else:
+            sel_len = flen(pads.sel_n)
+        gpio = Signal(sel_len + 1)
         gpio_load = Signal()
         self.sync += If(gpio_load, gpio.eq(bus.dat_w))
         if hasattr(pads, "rst"):