diff --git a/RELEASE_NOTES.rst b/RELEASE_NOTES.rst
index ede3e4d3c..8055694b9 100644
--- a/RELEASE_NOTES.rst
+++ b/RELEASE_NOTES.rst
@@ -3,6 +3,13 @@
 Release notes
 =============
 
+1.1 (unreleased)
+----------------
+
+* TCA6424A.set converts the "outputs" value to little-endian before programming
+  it into the registers.
+
+
 1.0
 ---
 
diff --git a/artiq/coredevice/i2c.py b/artiq/coredevice/i2c.py
index fb37a2aa6..da3fa6269 100644
--- a/artiq/coredevice/i2c.py
+++ b/artiq/coredevice/i2c.py
@@ -108,5 +108,10 @@ class TCA6424A:
 
         A bit set to 1 means the TTL is an output.
         """
+        outputs_le = (
+            ((outputs & 0xff0000) >> 16) |
+            (outputs & 0x00ff00) |
+            (outputs & 0x0000ff) << 16)
+
         self._write24(0x8c, 0)  # set all directions to output
-        self._write24(0x84, outputs)  # set levels
+        self._write24(0x84, outputs_le)  # set levels