diff --git a/contrib/linearize/example-linearize.cfg b/contrib/linearize/example-linearize.cfg
index 2315898bf..84129f204 100644
--- a/contrib/linearize/example-linearize.cfg
+++ b/contrib/linearize/example-linearize.cfg
@@ -5,13 +5,13 @@ rpcpassword=somepassword
 host=127.0.0.1
 
 #mainnet default
-port=8332
+port=9332
 
 #testnet default
-#port=18332
+#port=19332
 
 #regtest default
-#port=18443
+#port=19443
 
 # bootstrap.dat hashlist settings (linearize-hashes)
 max_height=313000
diff --git a/contrib/qos/README.md b/contrib/qos/README.md
index 0ded87c58..2d1cf7e5b 100644
--- a/contrib/qos/README.md
+++ b/contrib/qos/README.md
@@ -1,5 +1,5 @@
 ### QoS (Quality of service) ###
 
-This is a Linux bash script that will set up tc to limit the outgoing bandwidth for connections to the Bitcoin network. It limits outbound TCP traffic with a source or destination port of 8333, but not if the destination IP is within a LAN.
+This is a Linux bash script that will set up tc to limit the outgoing bandwidth for connections to the Litecoin network. It limits outbound TCP traffic with a source or destination port of 9333, but not if the destination IP is within a LAN (defined as 192.168.x.x).
 
-This means one can have an always-on bitcoind instance running, and another local bitcoind/bitcoin-qt instance which connects to this node and receives blocks from it.
+This means one can have an always-on litecoind instance running, and another local litecoind/litecoin-qt instance which connects to this node and receives blocks from it.
diff --git a/contrib/qos/tc.sh b/contrib/qos/tc.sh
index 5f9b87d9b..9e7445c3f 100644
--- a/contrib/qos/tc.sh
+++ b/contrib/qos/tc.sh
@@ -9,7 +9,7 @@ export LC_ALL=C
 IF="eth0"
 #limit of the network interface in question
 LINKCEIL="1gbit"
-#limit outbound Bitcoin protocol traffic to this rate
+#limit outbound Litecoin protocol traffic to this rate
 LIMIT="160kbit"
 #defines the IPv4 address space for which you wish to disable rate limiting
 LOCALNET_V4="192.168.0.0/16"
@@ -47,16 +47,16 @@ fi
 #	ret=$?
 #done
 
-#limit outgoing traffic to and from port 8333. but not when dealing with a host on the local network
+#limit outgoing traffic to and from port 9333. but not when dealing with a host on the local network
 #	(defined by $LOCALNET_V4 and $LOCALNET_V6)
 #	--set-mark marks packages matching these criteria with the number "2" (v4)
 #	--set-mark marks packages matching these criteria with the number "4" (v6)
 #	these packets are filtered by the tc filter with "handle 2"
 #	this filter sends the packages into the 1:11 class, and this class is limited to ${LIMIT}
-iptables -t mangle -A OUTPUT -p tcp -m tcp --dport 8333 ! -d ${LOCALNET_V4} -j MARK --set-mark 0x2
-iptables -t mangle -A OUTPUT -p tcp -m tcp --sport 8333 ! -d ${LOCALNET_V4} -j MARK --set-mark 0x2
+iptables -t mangle -A OUTPUT -p tcp -m tcp --dport 9333 ! -d ${LOCALNET_V4} -j MARK --set-mark 0x2
+iptables -t mangle -A OUTPUT -p tcp -m tcp --sport 9333 ! -d ${LOCALNET_V4} -j MARK --set-mark 0x2
 
 if [ ! -z "${LOCALNET_V6}" ] ; then
-	ip6tables -t mangle -A OUTPUT -p tcp -m tcp --dport 8333 ! -d ${LOCALNET_V6} -j MARK --set-mark 0x4
-	ip6tables -t mangle -A OUTPUT -p tcp -m tcp --sport 8333 ! -d ${LOCALNET_V6} -j MARK --set-mark 0x4
+	ip6tables -t mangle -A OUTPUT -p tcp -m tcp --dport 9333 ! -d ${LOCALNET_V6} -j MARK --set-mark 0x4
+	ip6tables -t mangle -A OUTPUT -p tcp -m tcp --sport 9333 ! -d ${LOCALNET_V6} -j MARK --set-mark 0x4
 fi
diff --git a/contrib/seeds/generate-seeds.py b/contrib/seeds/generate-seeds.py
index fe7cd1d59..ab96d3374 100755
--- a/contrib/seeds/generate-seeds.py
+++ b/contrib/seeds/generate-seeds.py
@@ -128,10 +128,10 @@ def main():
     g.write(' * IPv4 as well as onion addresses are wrapped inside an IPv6 address accordingly.\n')
     g.write(' */\n')
     with open(os.path.join(indir,'nodes_main.txt'), 'r', encoding="utf8") as f:
-        process_nodes(g, f, 'pnSeed6_main', 8333)
+        process_nodes(g, f, 'pnSeed6_main', 9333)
     g.write('\n')
     with open(os.path.join(indir,'nodes_test.txt'), 'r', encoding="utf8") as f:
-        process_nodes(g, f, 'pnSeed6_test', 18333)
+        process_nodes(g, f, 'pnSeed6_test', 19335)
     g.write('#endif // BITCOIN_CHAINPARAMSSEEDS_H\n')
 
 if __name__ == '__main__':
diff --git a/doc/REST-interface.md b/doc/REST-interface.md
index 02a665008..001f6d763 100644
--- a/doc/REST-interface.md
+++ b/doc/REST-interface.md
@@ -72,7 +72,7 @@ https://github.com/bitcoin/bips/blob/master/bip-0064.mediawiki
 
 Example:
 ```
-$ curl localhost:18332/rest/getutxos/checkmempool/b2cdfd7b89def827ff8af7cd9bff7627ff72e5e8b0f71210f92ea7a4000c5d75-0.json 2>/dev/null | json_pp
+$ curl localhost:19332/rest/getutxos/checkmempool/b2cdfd7b89def827ff8af7cd9bff7627ff72e5e8b0f71210f92ea7a4000c5d75-0.json 2>/dev/null | json_pp
 {
    "chainHeight" : 325347,
    "chaintipHash" : "00000000fb01a7f3745a717f8caebee056c484e6e0bfe4a9591c235bb70506fb",
@@ -114,4 +114,4 @@ Only supports JSON as output format.
 
 Risks
 -------------
-Running a web browser on the same node with a REST enabled bitcoind can be a risk. Accessing prepared XSS websites could read out tx/block data of your node by placing links like `<script src="http://127.0.0.1:8332/rest/tx/1234567890.json">` which might break the nodes privacy.
+Running a web browser on the same node with a REST enabled bitcoind can be a risk. Accessing prepared XSS websites could read out tx/block data of your node by placing links like `<script src="http://127.0.0.1:9332/rest/tx/1234567890.json">` which might break the nodes privacy.
diff --git a/doc/developer-notes.md b/doc/developer-notes.md
index f765346cd..5f0d4088c 100644
--- a/doc/developer-notes.md
+++ b/doc/developer-notes.md
@@ -392,7 +392,7 @@ Threads
 
 - ThreadMapPort : Universal plug-and-play startup/shutdown
 
-- ThreadSocketHandler : Sends/Receives data from peers on port 8333.
+- ThreadSocketHandler : Sends/Receives data from peers on port 9333.
 
 - ThreadOpenAddedConnections : Opens network connections to added nodes.
 
@@ -402,7 +402,7 @@ Threads
 
 - DumpAddresses : Dumps IP addresses of nodes to peers.dat.
 
-- ThreadRPCServer : Remote procedure call handler, listens on port 8332 for connections and services them.
+- ThreadRPCServer : Remote procedure call handler, listens on port 9332 for connections and services them.
 
 - Shutdown : Does an orderly shutdown of everything.
 
diff --git a/doc/tor.md b/doc/tor.md
index cfb7f1666..48d7fe6cd 100644
--- a/doc/tor.md
+++ b/doc/tor.md
@@ -45,11 +45,11 @@ config file): *Needed for Tor version 0.2.7.0 and older versions of Tor only. Fo
 versions of Tor see [Section 3](#3-automatically-listen-on-tor).*
 
 	HiddenServiceDir /var/lib/tor/bitcoin-service/
-	HiddenServicePort 8333 127.0.0.1:8333
-	HiddenServicePort 18333 127.0.0.1:18333
+	HiddenServicePort 9333 127.0.0.1:9333
+	HiddenServicePort 19333 127.0.0.1:19333
 
 The directory can be different of course, but (both) port numbers should be equal to
-your bitcoind's P2P listen port (8333 by default).
+your bitcoind's P2P listen port (9333 by default).
 
 	-externalip=X   You can tell bitcoin about its publicly reachable address using
 	                this option, and this can be a .onion address. Given the above
@@ -84,7 +84,7 @@ as well, use `discover` instead:
 
 	./bitcoind ... -discover
 
-and open port 8333 on your firewall (or use -upnp).
+and open port 9333 on your firewall (or use -upnp).
 
 If you only want to use Tor to reach .onion addresses, but not use it as a proxy
 for normal IPv4/IPv6 communication, use:
diff --git a/share/examples/bitcoin.conf b/share/examples/bitcoin.conf
index 6062d49c4..a423b70a3 100644
--- a/share/examples/bitcoin.conf
+++ b/share/examples/bitcoin.conf
@@ -44,11 +44,11 @@
 
 # Use as many addnode= settings as you like to connect to specific peers
 #addnode=69.164.218.197
-#addnode=10.0.0.2:8333
+#addnode=10.0.0.2:9333
 
 # Alternatively use as many connect= settings as you like to connect ONLY to specific peers
 #connect=69.164.218.197
-#connect=10.0.0.1:8333
+#connect=10.0.0.1:9333
 
 # Listening mode, enabled by default except when 'connect' is being used
 #listen=1
@@ -107,7 +107,7 @@
 #rpcallowip=2001:db8:85a3:0:0:8a2e:370:7334/96
 
 # Listen for RPC connections on this TCP port:
-#rpcport=8332
+#rpcport=9332
 
 # You can use Bitcoin or bitcoind to send commands to Bitcoin/bitcoind
 # running on another host using this option:
diff --git a/src/amount.h b/src/amount.h
index 47968e80b..bd3b6b07b 100644
--- a/src/amount.h
+++ b/src/amount.h
@@ -22,7 +22,7 @@ static const CAmount COIN = 100000000;
  * critical; in unusual circumstances like a(nother) overflow bug that allowed
  * for the creation of coins out of thin air modification could lead to a fork.
  * */
-static const CAmount MAX_MONEY = 21000000 * COIN;
+static const CAmount MAX_MONEY = 84000000 * COIN;
 inline bool MoneyRange(const CAmount& nValue) { return (nValue >= 0 && nValue <= MAX_MONEY); }
 
 #endif //  BITCOIN_AMOUNT_H
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index e967abafc..13b1b175c 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -51,7 +51,7 @@ static constexpr int32_t MAX_OUTBOUND_PEERS_TO_PROTECT_FROM_DISCONNECT = 4;
 /** Timeout for (unprotected) outbound peers to sync to our chainwork, in seconds */
 static constexpr int64_t CHAIN_SYNC_TIMEOUT = 20 * 60; // 20 minutes
 /** How frequently to check for stale tips, in seconds */
-static constexpr int64_t STALE_CHECK_INTERVAL = 10 * 60; // 10 minutes
+static constexpr int64_t STALE_CHECK_INTERVAL = 2.5 * 60; // 2.5 minutes
 /** How frequently to check for extra outbound peers and disconnect, in seconds */
 static constexpr int64_t EXTRA_PEER_CHECK_INTERVAL = 45;
 /** Minimum time an outbound-peer-eviction candidate must be connected for, in order to evict, in seconds */
@@ -1855,7 +1855,7 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
 
         // If the peer is old enough to have the old alert system, send it the final alert.
         if (pfrom->nVersion <= 70012) {
-            CDataStream finalAlert(ParseHex("60010000000000000000000000ffffff7f00000000ffffff7ffeffff7f01ffffff7f00000000ffffff7f00ffffff7f002f555247454e543a20416c657274206b657920636f6d70726f6d697365642c2075706772616465207265717569726564004630440220653febd6410f470f6bae11cad19c48413becb1ac2c17f908fd0fd53bdc3abd5202206d0e9c96fe88d4a0f01ed9dedae2b6f9e00da94cad0fecaae66ecf689bf71b50"), SER_NETWORK, PROTOCOL_VERSION);
+            CDataStream finalAlert(ParseHex("5c0100000015f7675900000000ffffff7f00000000ffffff7ffeffff7f0000000000ffffff7f00ffffff7f002f555247454e543a20416c657274206b657920636f6d70726f6d697365642c2075706772616465207265717569726564004630440220405f7e7572b176f3316d4e12deab75ad4ff978844f7a7bcd5ed06f6aa094eb6602207880fcc07d0a78e0f46f188d115e04ed4ad48980ea3572cb0e0cb97921048095"), SER_NETWORK, PROTOCOL_VERSION);
             connman->PushMessage(pfrom, CNetMsgMaker(nSendVersion).Make("alert", finalAlert));
         }
 
diff --git a/src/netaddress.cpp b/src/netaddress.cpp
index 58e45c2c0..a202000cb 100644
--- a/src/netaddress.cpp
+++ b/src/netaddress.cpp
@@ -11,8 +11,8 @@
 static const unsigned char pchIPv4[12] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff };
 static const unsigned char pchOnionCat[] = {0xFD,0x87,0xD8,0x7E,0xEB,0x43};
 
-// 0xFD + sha256("bitcoin")[0:5]
-static const unsigned char g_internal_prefix[] = { 0xFD, 0x6B, 0x88, 0xC0, 0x87, 0x24 };
+// 0xFD + sha256("litecoin")[0:5]
+static const unsigned char g_internal_prefix[] = { 0xFD, 0x6C, 0xE9, 0xFE, 0x45, 0x49 };
 
 CNetAddr::CNetAddr()
 {
diff --git a/src/pow.cpp b/src/pow.cpp
index 1414d3756..d82bdaf58 100644
--- a/src/pow.cpp
+++ b/src/pow.cpp
@@ -38,9 +38,17 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
     }
 
     // Go back by what we want to be 14 days worth of blocks
-    int nHeightFirst = pindexLast->nHeight - (params.DifficultyAdjustmentInterval()-1);
-    assert(nHeightFirst >= 0);
-    const CBlockIndex* pindexFirst = pindexLast->GetAncestor(nHeightFirst);
+    // Litecoin: This fixes an issue where a 51% attack can change difficulty at will.
+    // Go back the full period unless it's the first retarget after genesis. Code courtesy of Art Forz
+    int blockstogoback = params.DifficultyAdjustmentInterval()-1;
+    if ((pindexLast->nHeight+1) != params.DifficultyAdjustmentInterval())
+        blockstogoback = params.DifficultyAdjustmentInterval();
+
+    // Go back by what we want to be 14 days worth of blocks
+    const CBlockIndex* pindexFirst = pindexLast;
+    for (int i = 0; pindexFirst && i < blockstogoback; i++)
+        pindexFirst = pindexFirst->pprev;
+
     assert(pindexFirst);
 
     return CalculateNextWorkRequired(pindexLast, pindexFirst->GetBlockTime(), params);
@@ -59,11 +67,19 @@ unsigned int CalculateNextWorkRequired(const CBlockIndex* pindexLast, int64_t nF
         nActualTimespan = params.nPowTargetTimespan*4;
 
     // Retarget
-    const arith_uint256 bnPowLimit = UintToArith256(params.powLimit);
     arith_uint256 bnNew;
+    arith_uint256 bnOld;
     bnNew.SetCompact(pindexLast->nBits);
+    bnOld = bnNew;
+    // Litecoin: intermediate uint256 can overflow by 1 bit
+    const arith_uint256 bnPowLimit = UintToArith256(params.powLimit);
+    bool fShift = bnNew.bits() > bnPowLimit.bits() - 1;
+    if (fShift)
+        bnNew >>= 1;
     bnNew *= nActualTimespan;
     bnNew /= params.nPowTargetTimespan;
+    if (fShift)
+        bnNew <<= 1;
 
     if (bnNew > bnPowLimit)
         bnNew = bnPowLimit;
diff --git a/src/rpc/net.cpp b/src/rpc/net.cpp
index a5f590757..2ef36a076 100644
--- a/src/rpc/net.cpp
+++ b/src/rpc/net.cpp
@@ -226,8 +226,8 @@ static UniValue addnode(const JSONRPCRequest& request)
                 },
                 RPCResults{},
                 RPCExamples{
-                    HelpExampleCli("addnode", "\"192.168.0.6:8333\" \"onetry\"")
-            + HelpExampleRpc("addnode", "\"192.168.0.6:8333\", \"onetry\"")
+                    HelpExampleCli("addnode", "\"192.168.0.6:9333\" \"onetry\"")
+            + HelpExampleRpc("addnode", "\"192.168.0.6:9333\", \"onetry\"")
                 },
             }.ToString());
 
@@ -320,7 +320,7 @@ static UniValue getaddednodeinfo(const JSONRPCRequest& request)
             "    \"connected\" : true|false,          (boolean) If connected\n"
             "    \"addresses\" : [                    (list of objects) Only when connected = true\n"
             "       {\n"
-            "         \"address\" : \"192.168.0.201:8333\",  (string) The bitcoin server IP and port we're connected to\n"
+            "         \"address\" : \"192.168.0.201:9333\",  (string) The litecoin server IP and port we're connected to\n"
             "         \"connected\" : \"outbound\"           (string) connection, inbound or outbound\n"
             "       }\n"
             "     ]\n"
diff --git a/src/rpc/server.cpp b/src/rpc/server.cpp
index 6ebde86b5..c7e53f8c2 100644
--- a/src/rpc/server.cpp
+++ b/src/rpc/server.cpp
@@ -590,7 +590,7 @@ std::string HelpExampleCli(const std::string& methodname, const std::string& arg
 std::string HelpExampleRpc(const std::string& methodname, const std::string& args)
 {
     return "> curl --user myusername --data-binary '{\"jsonrpc\": \"1.0\", \"id\":\"curltest\", "
-        "\"method\": \"" + methodname + "\", \"params\": [" + args + "] }' -H 'content-type: text/plain;' http://127.0.0.1:8332/\n";
+        "\"method\": \"" + methodname + "\", \"params\": [" + args + "] }' -H 'content-type: text/plain;' http://127.0.0.1:9332/\n";
 }
 
 void RPCSetTimerInterfaceIfUnset(RPCTimerInterface *iface)
diff --git a/src/test/compress_tests.cpp b/src/test/compress_tests.cpp
index e686c0516..c5aa60856 100644
--- a/src/test/compress_tests.cpp
+++ b/src/test/compress_tests.cpp
@@ -20,7 +20,7 @@
 #define NUM_MULTIPLES_1BTC 10000
 
 // amounts 50 .. 21000000
-#define NUM_MULTIPLES_50BTC 420000
+#define NUM_MULTIPLES_50BTC 1680000
 
 BOOST_FIXTURE_TEST_SUITE(compress_tests, BasicTestingSetup)
 
@@ -44,7 +44,7 @@ BOOST_AUTO_TEST_CASE(compress_amounts)
     BOOST_CHECK(TestPair(         CENT,       0x7));
     BOOST_CHECK(TestPair(         COIN,       0x9));
     BOOST_CHECK(TestPair(      50*COIN,      0x32));
-    BOOST_CHECK(TestPair(21000000*COIN, 0x1406f40));
+    BOOST_CHECK(TestPair(84000000*COIN, 0x501BD00));
 
     for (uint64_t i = 1; i <= NUM_MULTIPLES_UNIT; i++)
         BOOST_CHECK(TestEncode(i));
diff --git a/src/test/miner_tests.cpp b/src/test/miner_tests.cpp
index 167ce36bf..1066c2a6a 100644
--- a/src/test/miner_tests.cpp
+++ b/src/test/miner_tests.cpp
@@ -381,7 +381,7 @@ BOOST_AUTO_TEST_CASE(CreateNewBlock_validity)
     }
     BOOST_CHECK(pblocktemplate = AssemblerForTest(chainparams).CreateNewBlock(scriptPubKey));
     // Extend to a 210000-long block chain.
-    while (chainActive.Tip()->nHeight < 210000) {
+    while (chainActive.Tip()->nHeight < 840000) {
         CBlockIndex* prev = chainActive.Tip();
         CBlockIndex* next = new CBlockIndex();
         next->phashBlock = new uint256(InsecureRand256());
diff --git a/src/test/netbase_tests.cpp b/src/test/netbase_tests.cpp
index 0d557cff1..367b48409 100644
--- a/src/test/netbase_tests.cpp
+++ b/src/test/netbase_tests.cpp
@@ -67,7 +67,7 @@ BOOST_AUTO_TEST_CASE(netbase_properties)
     BOOST_CHECK(ResolveIP("8.8.8.8").IsRoutable());
     BOOST_CHECK(ResolveIP("2001::1").IsRoutable());
     BOOST_CHECK(ResolveIP("127.0.0.1").IsValid());
-    BOOST_CHECK(CreateInternal("FD6B:88C0:8724:edb1:8e4:3588:e546:35ca").IsInternal());
+    BOOST_CHECK(CreateInternal("FD6C:E9FE:4549:edb1:8e4:3588:e546:35ca").IsInternal());
     BOOST_CHECK(CreateInternal("bar.com").IsInternal());
 
 }
@@ -116,9 +116,9 @@ BOOST_AUTO_TEST_CASE(netbase_lookupnumeric)
     BOOST_CHECK(TestParse(":::", "[::]:0"));
 
     // verify that an internal address fails to resolve
-    BOOST_CHECK(TestParse("[fd6b:88c0:8724:1:2:3:4:5]", "[::]:0"));
+    BOOST_CHECK(TestParse("[fd6c:e9fe:4549:1:2:3:4:5]", "[::]:0"));
     // and that a one-off resolves correctly
-    BOOST_CHECK(TestParse("[fd6c:88c0:8724:1:2:3:4:5]", "[fd6c:88c0:8724:1:2:3:4:5]:65535"));
+    BOOST_CHECK(TestParse("[fd6d:e9fe:4549:1:2:3:4:5]", "[fd6d:e9fe:4549:1:2:3:4:5]:65535"));
 }
 
 BOOST_AUTO_TEST_CASE(onioncat_test)
diff --git a/src/timedata.h b/src/timedata.h
index b165ecde2..aa46ae40b 100644
--- a/src/timedata.h
+++ b/src/timedata.h
@@ -10,7 +10,7 @@
 #include <stdint.h>
 #include <vector>
 
-static const int64_t DEFAULT_MAX_TIME_ADJUSTMENT = 70 * 60;
+static const int64_t DEFAULT_MAX_TIME_ADJUSTMENT = 35 * 60;
 
 class CNetAddr;
 
diff --git a/src/validation.cpp b/src/validation.cpp
index a493efd39..e5f512b36 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1871,8 +1871,10 @@ bool CChainState::ConnectBlock(const CBlock& block, CValidationState& state, CBl
     // Now that the whole chain is irreversibly beyond that time it is applied to all blocks except the
     // two in the chain that violate it. This prevents exploiting the issue against nodes during their
     // initial block download.
-    bool fEnforceBIP30 = !((pindex->nHeight==91842 && pindex->GetBlockHash() == uint256S("0x00000000000a4d0a398161ffc163c503763b1f4360639393e0e4c8e300e0caec")) ||
-                           (pindex->nHeight==91880 && pindex->GetBlockHash() == uint256S("0x00000000000743f190a18c5577a3c2d2a1f610ae9601ac046a38084ccb7cd721")));
+    
+    bool fEnforceBIP30 = true;
+    //bool fEnforceBIP30 = !((pindex->nHeight==91842 && pindex->GetBlockHash() == uint256S("0x00000000000a4d0a398161ffc163c503763b1f4360639393e0e4c8e300e0caec")) ||
+    //                       (pindex->nHeight==91880 && pindex->GetBlockHash() == uint256S("0x00000000000743f190a18c5577a3c2d2a1f610ae9601ac046a38084ccb7cd721")));
 
     // Once BIP34 activated it was not possible to create new duplicate coinbases and thus other than starting
     // with the 2 existing duplicate coinbase pairs, not possible to create overwriting txs.  But by the
@@ -3263,6 +3265,10 @@ static bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationSta
             return state.Invalid(false, REJECT_OBSOLETE, strprintf("bad-version(0x%08x)", block.nVersion),
                                  strprintf("rejected nVersion=0x%08x block", block.nVersion));
 
+    if (block.nVersion < VERSIONBITS_TOP_BITS && IsWitnessEnabled(pindexPrev, consensusParams))
+        return state.Invalid(false, REJECT_OBSOLETE, strprintf("bad-version(0x%08x)", block.nVersion),
+                                 strprintf("rejected nVersion=0x%08x block", block.nVersion));
+
     return true;
 }
 
diff --git a/src/validation.h b/src/validation.h
index 65a378d8b..56cf98d96 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -196,7 +196,7 @@ static const unsigned int MIN_BLOCKS_TO_KEEP = 288;
 /** Minimum blocks required to signal NODE_NETWORK_LIMITED */
 static const unsigned int NODE_NETWORK_LIMITED_MIN_BLOCKS = 288;
 
-static const signed int DEFAULT_CHECKBLOCKS = 6;
+static const signed int DEFAULT_CHECKBLOCKS = 6 * 4;
 static const unsigned int DEFAULT_CHECKLEVEL = 3;
 
 // Require that user allocate at least 550 MiB for block & undo files (blk???.dat and rev???.dat)
diff --git a/src/version.h b/src/version.h
index d932b512d..36fe5a8e9 100644
--- a/src/version.h
+++ b/src/version.h
@@ -15,7 +15,7 @@ static const int PROTOCOL_VERSION = 70015;
 static const int INIT_PROTO_VERSION = 209;
 
 //! In this version, 'getheaders' was introduced.
-static const int GETHEADERS_VERSION = 31800;
+static const int GETHEADERS_VERSION = 70002;
 
 //! disconnect from peers older than this proto version
 static const int MIN_PEER_PROTO_VERSION = GETHEADERS_VERSION;
diff --git a/test/functional/feature_nulldummy.py b/test/functional/feature_nulldummy.py
index eb76089d9..d68c52c3a 100755
--- a/test/functional/feature_nulldummy.py
+++ b/test/functional/feature_nulldummy.py
@@ -21,6 +21,7 @@ from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import assert_equal, assert_raises_rpc_error, bytes_to_hex_str
 
 NULLDUMMY_ERROR = "non-mandatory-script-verify-flag (Dummy CHECKMULTISIG argument must be zero) (code 64)"
+VB_TOP_BITS = 0x20000000
 
 def trueDummy(tx):
     scriptSig = CScript(tx.vin[0].scriptSig)
@@ -96,11 +97,11 @@ class NULLDUMMYTest(BitcoinTestFramework):
         self.log.info("Test 6: NULLDUMMY compliant base/witness transactions should be accepted to mempool and in block after activation [432]")
         for i in test6txs:
             self.nodes[0].sendrawtransaction(bytes_to_hex_str(i.serialize_with_witness()), True)
-        self.block_submit(self.nodes[0], test6txs, True, True)
+        self.block_submit(self.nodes[0], test6txs, True, True, VB_TOP_BITS)
 
-    def block_submit(self, node, txs, witness=False, accept=False):
+    def block_submit(self, node, txs, witness=False, accept=False, version=4):
         block = create_block(self.tip, create_coinbase(self.lastblockheight + 1), self.lastblocktime + 1)
-        block.nVersion = 4
+        block.nVersion = version
         for tx in txs:
             tx.rehash()
             block.vtx.append(tx)
diff --git a/test/functional/feature_proxy.py b/test/functional/feature_proxy.py
index f042adb7a..a309d5649 100755
--- a/test/functional/feature_proxy.py
+++ b/test/functional/feature_proxy.py
@@ -121,24 +121,24 @@ class ProxyTest(BitcoinTestFramework):
 
         if test_onion:
             # Test: outgoing onion connection through node
-            node.addnode("bitcoinostk4e4re.onion:8333", "onetry")
+            node.addnode("bitcoinostk4e4re.onion:9333", "onetry")
             cmd = proxies[2].queue.get()
             assert(isinstance(cmd, Socks5Command))
             assert_equal(cmd.atyp, AddressType.DOMAINNAME)
             assert_equal(cmd.addr, b"bitcoinostk4e4re.onion")
-            assert_equal(cmd.port, 8333)
+            assert_equal(cmd.port, 9333)
             if not auth:
                 assert_equal(cmd.username, None)
                 assert_equal(cmd.password, None)
             rv.append(cmd)
 
         # Test: outgoing DNS name connection through node
-        node.addnode("node.noumenon:8333", "onetry")
+        node.addnode("node.noumenon:9333", "onetry")
         cmd = proxies[3].queue.get()
         assert(isinstance(cmd, Socks5Command))
         assert_equal(cmd.atyp, AddressType.DOMAINNAME)
         assert_equal(cmd.addr, b"node.noumenon")
-        assert_equal(cmd.port, 8333)
+        assert_equal(cmd.port, 9333)
         if not auth:
             assert_equal(cmd.username, None)
             assert_equal(cmd.password, None)
diff --git a/test/functional/p2p_segwit.py b/test/functional/p2p_segwit.py
index 62b12507e..903ced59e 100755
--- a/test/functional/p2p_segwit.py
+++ b/test/functional/p2p_segwit.py
@@ -201,7 +201,7 @@ class SegWitTest(BitcoinTestFramework):
 
     # Helper functions
 
-    def build_next_block(self, version=4):
+    def build_next_block(self, nVersion=VB_TOP_BITS):
         """Build a block on top of node0's tip."""
         tip = self.nodes[0].getbestblockhash()
         height = self.nodes[0].getblockcount() + 1
@@ -1922,6 +1922,12 @@ class SegWitTest(BitcoinTestFramework):
     def test_upgrade_after_activation(self):
         """Test the behavior of starting up a segwit-aware node after the softfork has activated."""
 
+        print ("\tTesting rejection of block.nVersion < BIP9_TOP_BITS blocks")
+        block = self.build_next_block(nVersion=4)
+        block.solve()
+        resp = self.nodes[0].submitblock(bytes_to_hex_str(block.serialize(True)))
+        assert_equal(resp, 'bad-version(0x00000004)')
+
         # Restart with the new binary
         self.stop_node(2)
         self.start_node(2, extra_args=["-vbparams=segwit:0:999999999999"])