diff --git a/artiq/coredevice/i2c.py b/artiq/coredevice/i2c.py
index 55148402a..d834117f5 100644
--- a/artiq/coredevice/i2c.py
+++ b/artiq/coredevice/i2c.py
@@ -109,4 +109,4 @@ class TCA6424A:
         A bit set to 1 means the TTL is an output.
         """
         self._write24(0x8c, 0)  # set all directions to output
-        self._write24(0x84, output)  # set levels
+        self._write24(0x84, outputs)  # set levels