diff --git a/src/include/gpxe/netdevice.h b/src/include/gpxe/netdevice.h
index d82c6d8f..2cbd0efb 100644
--- a/src/include/gpxe/netdevice.h
+++ b/src/include/gpxe/netdevice.h
@@ -19,10 +19,10 @@ struct ll_protocol;
 struct device;
 
 /** Maximum length of a link-layer address */
-#define MAX_LL_ADDR_LEN 6
+#define MAX_LL_ADDR_LEN 20
 
 /** Maximum length of a link-layer header */
-#define MAX_LL_HEADER_LEN 16
+#define MAX_LL_HEADER_LEN 32
 
 /** Maximum length of a network-layer address */
 #define MAX_NET_ADDR_LEN 4