diff --git a/sys/net/if.c b/sys/net/if.c
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -149,6 +149,15 @@
 CTASSERT(__offsetof(struct ifreq, ifr_ifru) ==
     __offsetof(struct ifreq32, ifr_ifru));
 
+struct ifdrv32 {
+	char		ifd_name[IFNAMSIZ];
+	uint32_t	ifd_cmd;
+	uint32_t	ifd_len;
+	uint32_t	ifd_data;
+};
+#define SIOCSDRVSPEC32	_IOC_NEWTYPE(SIOCSDRVSPEC, struct ifdrv32)
+#define SIOCGDRVSPEC32	_IOC_NEWTYPE(SIOCGDRVSPEC, struct ifdrv32)
+
 struct ifgroupreq32 {
 	char	ifgr_name[IFNAMSIZ];
 	u_int	ifgr_len;
@@ -2926,11 +2935,13 @@
 #ifdef COMPAT_FREEBSD32
 	union {
 		struct ifconf ifc;
+		struct ifdrv ifd;
 		struct ifmediareq ifmr;
 	} thunk;
 	caddr_t saved_data;
 	u_long saved_cmd;
 	struct ifconf32 *ifc32;
+	struct ifdrv32 *ifd32;
 	struct ifmediareq32 *ifmr32;
 #endif
 	struct ifnet *ifp;
@@ -2962,6 +2973,17 @@
 		data = (caddr_t)&thunk.ifc;
 		cmd = SIOCGIFCONF;
 		break;
+	case SIOCGDRVSPEC32:
+	case SIOCSDRVSPEC32:
+		ifd32 = (struct ifdrv32 *)data;
+		memcpy(thunk.ifd.ifd_name, ifd32->ifd_name,
+		    sizeof(thunk.ifd.ifd_name));
+		thunk.ifd.ifd_cmd = ifd32->ifd_cmd;
+		thunk.ifd.ifd_len = ifd32->ifd_len;
+		thunk.ifd.ifd_data = PTRIN(ifd32->ifd_data);
+		data = (caddr_t)&thunk.ifd;
+		cmd = _IOC_NEWTYPE(cmd, struct ifdrv);
+		break;
 	case SIOCGIFMEDIA32:
 	case SIOCGIFXMEDIA32:
 		ifmr32 = (struct ifmediareq32 *)data;
@@ -3082,6 +3104,17 @@
 	case SIOCGIFCONF32:
 		ifc32->ifc_len = thunk.ifc.ifc_len;
 		break;
+	case SIOCGDRVSPEC32:
+		/*
+		 * SIOCGDRVSPEC is IOWR, but nothing actually touches
+		 * the struct so just assert that ifd_len (the only
+		 * field it might make sense to update) hasn't
+		 * changed.
+		 */
+		KASSERT(thunk.ifd.ifd_len == ifd32->ifd_len,
+		    ("ifd_len was updated %u -> %zu", ifd32->ifd_len,
+			thunk.ifd.ifd_len));
+		break;
 	case SIOCGIFMEDIA32:
 	case SIOCGIFXMEDIA32:
 		ifmr32->ifm_current = thunk.ifmr.ifm_current;