diff --git a/artiq/firmware/runtime/ethmac.rs b/artiq/firmware/runtime/ethmac.rs
index 23047bab0..c31e64ad7 100644
--- a/artiq/firmware/runtime/ethmac.rs
+++ b/artiq/firmware/runtime/ethmac.rs
@@ -26,7 +26,7 @@ impl Device for EthernetDevice {
     fn limits(&self) -> DeviceLimits {
         let mut limits = DeviceLimits::default();
         limits.max_transmission_unit = 1500;
-        limits.max_burst_size = Some(RX_BUFFERS.len());
+        limits.max_burst_size = Some(RX_BUFFERS.len() - 1);
         limits
     }