diff --git a/rtl/hub_core.v b/rtl/hub_core.v
index bc7be5f..e4852de 100644
--- a/rtl/hub_core.v
+++ b/rtl/hub_core.v
@@ -28,6 +28,7 @@ module hub_core (
 	reg jam, activity;
 	reg [PORT_BITS - 1:0] active_port;
 	reg [PORT_COUNT - 1:0] tx_en_next, tx_er_next;
+	(* mem2reg *)
 	reg [3:0] txd_next [PORT_COUNT - 1:0];
 
 	always @(*) begin
diff --git a/rtl/mii_elastic_buffer.v b/rtl/mii_elastic_buffer.v
index 332b3b7..4a54fe5 100644
--- a/rtl/mii_elastic_buffer.v
+++ b/rtl/mii_elastic_buffer.v
@@ -47,6 +47,7 @@ module mii_elastic_buffer (
 
 	integer i;
 	reg [BUF_SIZE - 1:0] valid, valid_next, err, err_next;
+	(* mem2reg *)
 	reg [3:0] data [BUF_SIZE - 1:0], data_next [BUF_SIZE - 1:0];
 	reg shift, overflow_next, underflow_next;
 	reg in, in_next, out, out_next, rx_ce_last, rx_dv_last;