diff --git a/dll/windivert_helper.c b/dll/windivert_helper.c
index 9abab7d..833f79a 100644
--- a/dll/windivert_helper.c
+++ b/dll/windivert_helper.c
@@ -424,6 +424,11 @@ extern UINT WinDivertHelperCalcChecksums(PVOID pPacket, UINT packetLen,
     UINT payload_len, checksum_len;
     UINT count = 0;
 
+    if ((flags & 0x1F) == 0x1F)
+    {
+        return 0;
+    }
+
     WinDivertHelperParsePacket(pPacket, packetLen, &ip_header, &ipv6_header,
         &icmp_header, &icmpv6_header, &tcp_header, &udp_header, NULL,
         &payload_len);
diff --git a/examples/netdump/netdump.c b/examples/netdump/netdump.c
index 8447602..39ac27d 100644
--- a/examples/netdump/netdump.c
+++ b/examples/netdump/netdump.c
@@ -52,6 +52,7 @@ int __cdecl main(int argc, char **argv)
     PWINDIVERT_ICMPV6HDR icmpv6_header;
     PWINDIVERT_TCPHDR tcp_header;
     PWINDIVERT_UDPHDR udp_header;
+    const char *err_str;
 
     // Check arguments.
     switch (argc)
@@ -68,7 +69,7 @@ int __cdecl main(int argc, char **argv)
             fprintf(stderr, "\t%s true\n", argv[0]);
             fprintf(stderr, "\t%s \"outbound and tcp.DstPort == 80\" 1000\n",
                 argv[0]);
-            fprintf(stderr, "\t%s \"inbound and tcp.Syn\" -4000\n", argv[0]);
+            fprintf(stderr, "\t%s \"inbound and tcp.Syn\" -400\n", argv[0]);
             exit(EXIT_FAILURE);
     }
 
@@ -80,9 +81,11 @@ int __cdecl main(int argc, char **argv)
         WINDIVERT_FLAG_SNIFF);
     if (handle == INVALID_HANDLE_VALUE)
     {
-        if (GetLastError() == ERROR_INVALID_PARAMETER)
+        if (GetLastError() == ERROR_INVALID_PARAMETER &&
+            !WinDivertHelperCheckFilter(argv[1], WINDIVERT_LAYER_NETWORK,
+                &err_str, NULL))
         {
-            fprintf(stderr, "error: filter syntax error\n");
+            fprintf(stderr, "error: invalid filter \"%s\"\n", err_str);
             exit(EXIT_FAILURE);
         }
         fprintf(stderr, "error: failed to open the WinDivert device (%d)\n",
@@ -114,6 +117,12 @@ int __cdecl main(int argc, char **argv)
                 GetLastError());
             continue;
         }
+
+        // Calculate checksums for outbound packets.
+        if (addr.Direction == WINDIVERT_DIRECTION_OUTBOUND)
+        {
+            WinDivertHelperCalcChecksums(packet, packet_len, 0);
+        }
        
         // Print info about the matching packet.
         WinDivertHelperParsePacket(packet, packet_len, &ip_header,
diff --git a/examples/netfilter/netfilter.c b/examples/netfilter/netfilter.c
index a355afd..6b968db 100644
--- a/examples/netfilter/netfilter.c
+++ b/examples/netfilter/netfilter.c
@@ -98,6 +98,7 @@ int __cdecl main(int argc, char **argv)
     PWINDIVERT_TCPHDR tcp_header;
     PWINDIVERT_UDPHDR udp_header;
     UINT payload_len;
+    const char *err_str;
     
     TCPPACKET reset0;
     PTCPPACKET reset = &reset0;
@@ -125,7 +126,7 @@ int __cdecl main(int argc, char **argv)
             fprintf(stderr, "\t%s true\n", argv[0]);
             fprintf(stderr, "\t%s \"outbound and tcp.DstPort == 80\" 1000\n",
                 argv[0]);
-            fprintf(stderr, "\t%s \"inbound and tcp.Syn\" -4000\n", argv[0]);
+            fprintf(stderr, "\t%s \"inbound and tcp.Syn\" -400\n", argv[0]);
             exit(EXIT_FAILURE);
     }
 
@@ -152,9 +153,11 @@ int __cdecl main(int argc, char **argv)
     handle = WinDivertOpen(argv[1], WINDIVERT_LAYER_NETWORK, priority, 0);
     if (handle == INVALID_HANDLE_VALUE)
     {
-        if (GetLastError() == ERROR_INVALID_PARAMETER)
+        if (GetLastError() == ERROR_INVALID_PARAMETER &&
+            !WinDivertHelperCheckFilter(argv[1], WINDIVERT_LAYER_NETWORK,
+                &err_str, NULL))
         {
-            fprintf(stderr, "error: filter syntax error\n");
+            fprintf(stderr, "error: invalid filter \"%s\"\n", err_str);
             exit(EXIT_FAILURE);
         }
         fprintf(stderr, "error: failed to open the WinDivert device (%d)\n",
diff --git a/examples/passthru/passthru.c b/examples/passthru/passthru.c
index 2b16be6..fe52562 100644
--- a/examples/passthru/passthru.c
+++ b/examples/passthru/passthru.c
@@ -106,7 +106,14 @@ static DWORD passthru(LPVOID arg)
                 GetLastError());
             continue;
         }
-       
+
+        // NOTE: Since WinDivert1.2 outbound packets are not guaranteed
+        //       to have correct checksums.
+        if (addr.Direction == WINDIVERT_DIRECTION_OUTBOUND)
+        {
+            WinDivertHelperCalcChecksums(packet, packet_len, 0);
+        }
+
         // Re-inject the matching packet.
         if (!WinDivertSend(handle, packet, packet_len, &addr, NULL))
         {
diff --git a/examples/webfilter/webfilter.c b/examples/webfilter/webfilter.c
index 3d2b9d1..d162ef1 100644
--- a/examples/webfilter/webfilter.c
+++ b/examples/webfilter/webfilter.c
@@ -188,6 +188,7 @@ int __cdecl main(int argc, char **argv)
             !BlackListPayloadMatch(blacklist, payload, (UINT16)payload_len))
         {
             // Packet does not match the blacklist; simply reinject it.
+            WinDivertHelperCalcChecksums(packet, packet_len, 0);
             if (!WinDivertSend(handle, packet, packet_len, &addr, NULL))
             {
                 fprintf(stderr, "warning: failed to reinject packet (%d)\n",
diff --git a/test/test.c b/test/test.c
index cc1ca13..500b1aa 100644
--- a/test/test.c
+++ b/test/test.c
@@ -321,6 +321,10 @@ read_failed:
         }
         buf_len = (UINT)iolen;
     }
+    if (addr.Direction == WINDIVERT_DIRECTION_OUTBOUND)
+    {
+        WinDivertHelperCalcChecksums(buf, buf_len, 0);
+    }
 
     // (4) Verify that the packet is the same.
     if (buf_len != packet_len)