diff --git a/src/openvpn/forward.c b/src/openvpn/forward.c
index c971c6bdb..6de6b4d49 100644
--- a/src/openvpn/forward.c
+++ b/src/openvpn/forward.c
@@ -480,10 +480,10 @@ check_fragment(struct context *c)
     struct link_socket_info *lsi = get_link_socket_info(c);
 
     /* OS MTU Hint? */
-    if (lsi->mtu_changed)
+    if (lsi->mtu_changed && lsi->lsa)
     {
         frame_adjust_path_mtu(&c->c2.frame_fragment, c->c2.link_socket->mtu,
-                              c->options.ce.proto);
+                              lsi->lsa->actual.dest.addr.sa.sa_family, lsi->proto);
         lsi->mtu_changed = false;
     }
 
@@ -1565,8 +1565,10 @@ process_outgoing_link(struct context *c)
              */
             if (c->options.shaper)
             {
-                shaper_wrote_bytes(&c->c2.shaper, BLEN(&c->c2.to_link)
-                                   + datagram_overhead(c->options.ce.proto));
+                int overhead = datagram_overhead(c->c2.to_link_addr->dest.addr.sa.sa_family,
+                                                 c->options.ce.proto);
+                shaper_wrote_bytes(&c->c2.shaper,
+                                   BLEN(&c->c2.to_link) + overhead);
             }
 
             /*
diff --git a/src/openvpn/socket.c b/src/openvpn/socket.c
index df7367469..93d2e61ec 100644
--- a/src/openvpn/socket.c
+++ b/src/openvpn/socket.c
@@ -44,17 +44,6 @@
 
 #include "memdbg.h"
 
-const int proto_overhead[] = { /* indexed by PROTO_x */
-    0,
-    IPv4_UDP_HEADER_SIZE, /* IPv4 */
-    IPv4_TCP_HEADER_SIZE,
-    IPv4_TCP_HEADER_SIZE,
-    IPv6_UDP_HEADER_SIZE, /* IPv6 */
-    IPv6_TCP_HEADER_SIZE,
-    IPv6_TCP_HEADER_SIZE,
-    IPv6_TCP_HEADER_SIZE,
-};
-
 /*
  * Convert sockflags/getaddr_flags into getaddr_flags
  */
@@ -1660,9 +1649,10 @@ socket_frame_init(const struct frame *frame, struct link_socket *sock)
  * to us by the OS.
  */
 void
-frame_adjust_path_mtu(struct frame *frame, int pmtu, int proto)
+frame_adjust_path_mtu(struct frame *frame, int pmtu, sa_family_t af, int proto)
 {
-    frame_set_mtu_dynamic(frame, pmtu - datagram_overhead(proto), SET_MTU_UPPER_BOUND);
+    frame_set_mtu_dynamic(frame, pmtu - datagram_overhead(af, proto),
+                          SET_MTU_UPPER_BOUND);
 }
 
 static void
diff --git a/src/openvpn/socket.h b/src/openvpn/socket.h
index cc1e0c366..936ef2623 100644
--- a/src/openvpn/socket.h
+++ b/src/openvpn/socket.h
@@ -300,7 +300,7 @@ void do_preresolve(struct context *c);
 
 void socket_adjust_frame_parameters(struct frame *frame, int proto);
 
-void frame_adjust_path_mtu(struct frame *frame, int pmtu, int proto);
+void frame_adjust_path_mtu(struct frame *frame, int pmtu, sa_family_t af, int proto);
 
 void link_socket_close(struct link_socket *sock);
 
@@ -579,18 +579,13 @@ const char *addr_family_name(int af);
 /*
  * Overhead added to packets by various protocols.
  */
-#define IPv4_UDP_HEADER_SIZE              28
-#define IPv4_TCP_HEADER_SIZE              40
-#define IPv6_UDP_HEADER_SIZE              48
-#define IPv6_TCP_HEADER_SIZE              60
-
-extern const int proto_overhead[];
-
 static inline int
-datagram_overhead(int proto)
+datagram_overhead(sa_family_t af, int proto)
 {
-    ASSERT(proto >= 0 && proto < PROTO_N);
-    return proto_overhead [proto];
+    int overhead = 0;
+    overhead += (proto == PROTO_UDP) ? 8 : 20;
+    overhead += (af == AF_INET) ? 20 : 40;
+    return overhead;
 }
 
 /*