diff --git a/artiq/gateware/targets/kc705_drtio_master.py b/artiq/gateware/targets/kc705_drtio_master.py
index a2e3213a8..c14d0ce68 100755
--- a/artiq/gateware/targets/kc705_drtio_master.py
+++ b/artiq/gateware/targets/kc705_drtio_master.py
@@ -34,6 +34,8 @@ class Master(MiniSoC, AMPSoC):
                          sdram_controller_type="minicon",
                          l2_size=128*1024,
                          ident=artiq_version,
+                         ethmac_nrxslots=4,
+                         ethmac_ntxslots=4,
                          **kwargs)
         AMPSoC.__init__(self)
 
diff --git a/artiq/gateware/targets/phaser.py b/artiq/gateware/targets/phaser.py
index 3923a6502..b2b10b0cd 100755
--- a/artiq/gateware/targets/phaser.py
+++ b/artiq/gateware/targets/phaser.py
@@ -169,6 +169,8 @@ class Phaser(MiniSoC, AMPSoC):
                          sdram_controller_type="minicon",
                          l2_size=128*1024,
                          ident=artiq_version,
+                         ethmac_nrxslots=4,
+                         ethmac_ntxslots=4,
                          **kwargs)
         AMPSoC.__init__(self)
         self.platform.toolchain.bitstream_commands.extend([