diff --git a/src/vnet/ip/icmp4.c b/src/vnet/ip/icmp4.c
index 3626e96..a598ca9 100644
--- a/src/vnet/ip/icmp4.c
+++ b/src/vnet/ip/icmp4.c
@@ -653,7 +653,13 @@
       ASSERT (p0->current_data == 0);
       ip0 = (void *) (p0->data + ip_offset);
       icmp0 = (void *) (p0->data + icmp_offset);
-      len0 = clib_net_to_host_u16 (ip0->length) - ip4_header_bytes (ip0);
+
+      /* if IP length has been specified, then calculate the length based on buffer */
+      if (ip0->length == 0)
+	len0 = vlib_buffer_length_in_chain (vm, p0) - icmp_offset;
+      else
+	len0 = clib_net_to_host_u16 (ip0->length) - icmp_offset;
+
       icmp0->checksum =
 	~ip_csum_fold (ip_incremental_checksum (0, icmp0, len0));
     }
diff --git a/src/vnet/tcp/tcp_pg.c b/src/vnet/tcp/tcp_pg.c
index 3be4592..45eaed9 100644
--- a/src/vnet/tcp/tcp_pg.c
+++ b/src/vnet/tcp/tcp_pg.c
@@ -77,7 +77,11 @@
       ASSERT (p0->current_data == 0);
       ip0 = (void *) (p0->data + ip_offset);
       tcp0 = (void *) (p0->data + tcp_offset);
-      tcp_len0 = clib_net_to_host_u16 (ip0->length) - sizeof (ip0[0]);
+      /* if IP length has been specified, then calculate the length based on buffer */
+      if (ip0->length == 0)
+	tcp_len0 = vlib_buffer_length_in_chain (vm, p0) - tcp_offset;
+      else
+	tcp_len0 = clib_net_to_host_u16 (ip0->length) - tcp_offset;
 
       /* Initialize checksum with header. */
       if (BITS (sum0) == 32)