diff --git a/artiq/firmware/libboard_artiq/hmc830_7043.rs b/artiq/firmware/libboard_artiq/hmc830_7043.rs
index 9a2aa5ac6..b44260ca8 100644
--- a/artiq/firmware/libboard_artiq/hmc830_7043.rs
+++ b/artiq/firmware/libboard_artiq/hmc830_7043.rs
@@ -270,8 +270,8 @@ pub mod hmc7043 {
                 else { write(channel_base, 0x51); }
             }
             else { write(channel_base, 0x10); }
-            write(channel_base + 0x1, (divider & 0x0ff) as u8);
-            write(channel_base + 0x2, ((divider & 0x700) >> 8) as u8);
+            write(channel_base + 0x1, (divider & 0xff) as u8);
+            write(channel_base + 0x2, ((divider & 0x0f) >> 8) as u8);
             write(channel_base + 0x3, aphase & 0x1f);
             write(channel_base + 0x4, dphase & 0x1f);