diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index d9a566646..88465d727 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -340,6 +340,12 @@ public:
         fTestnetToBeDeprecatedFieldRPC = false;
 
     }
+
+    void UpdateBIP9Parameters(Consensus::DeploymentPos d, int64_t nStartTime, int64_t nTimeout)
+    {
+        consensus.vDeployments[d].nStartTime = nStartTime;
+        consensus.vDeployments[d].nTimeout = nTimeout;
+    }
 };
 static CRegTestParams regTestParams;
 
@@ -370,3 +376,7 @@ void SelectParams(const std::string& network)
     pCurrentParams = &Params(network);
 }
 
+void UpdateRegtestBIP9Parameters(Consensus::DeploymentPos d, int64_t nStartTime, int64_t nTimeout)
+{
+    regTestParams.UpdateBIP9Parameters(d, nStartTime, nTimeout);
+}
diff --git a/src/chainparams.h b/src/chainparams.h
index 774593cfa..a9a4a224c 100644
--- a/src/chainparams.h
+++ b/src/chainparams.h
@@ -115,4 +115,9 @@ CChainParams& Params(const std::string& chain);
  */
 void SelectParams(const std::string& chain);
 
+/**
+ * Allows modifying the BIP9 regtest parameters.
+ */
+void UpdateRegtestBIP9Parameters(Consensus::DeploymentPos d, int64_t nStartTime, int64_t nTimeout);
+
 #endif // BITCOIN_CHAINPARAMS_H
diff --git a/src/init.cpp b/src/init.cpp
index 0ffc86e8b..d2176be92 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -411,6 +411,7 @@ std::string HelpMessage(HelpMessageMode mode)
         strUsage += HelpMessageOpt("-limitancestorsize=<n>", strprintf("Do not accept transactions whose size with all in-mempool ancestors exceeds <n> kilobytes (default: %u)", DEFAULT_ANCESTOR_SIZE_LIMIT));
         strUsage += HelpMessageOpt("-limitdescendantcount=<n>", strprintf("Do not accept transactions if any ancestor would have <n> or more in-mempool descendants (default: %u)", DEFAULT_DESCENDANT_LIMIT));
         strUsage += HelpMessageOpt("-limitdescendantsize=<n>", strprintf("Do not accept transactions if any ancestor would have more than <n> kilobytes of in-mempool descendants (default: %u).", DEFAULT_DESCENDANT_SIZE_LIMIT));
+        strUsage += HelpMessageOpt("-bip9params=deployment:start:end", "Use given start/end times for specified bip9 deployment (regtest-only)");
     }
     string debugCategories = "addrman, alert, bench, cmpctblock, coindb, db, http, libevent, lock, mempool, mempoolrej, net, proxy, prune, rand, reindex, rpc, selectcoins, tor, zmq"; // Don't translate these and qt below
     if (mode == HMM_BITCOIN_QT)
@@ -976,6 +977,8 @@ bool AppInit2(Config& config, boost::thread_group& threadGroup, CScheduler& sche
     if (GetBoolArg("-peerbloomfilters", DEFAULT_PEERBLOOMFILTERS))
         nLocalServices = ServiceFlags(nLocalServices | NODE_BLOOM);
 
+    nMaxTipAge = GetArg("-maxtipage", DEFAULT_MAX_TIP_AGE);
+
     fEnableReplacement = GetBoolArg("-mempoolreplacement", DEFAULT_ENABLE_REPLACEMENT);
     if ((!fEnableReplacement) && mapArgs.count("-mempoolreplacement")) {
         // Minimal effort at forwards compatibility
@@ -985,7 +988,40 @@ bool AppInit2(Config& config, boost::thread_group& threadGroup, CScheduler& sche
         fEnableReplacement = (std::find(vstrReplacementModes.begin(), vstrReplacementModes.end(), "fee") != vstrReplacementModes.end());
     }
 
-    nMaxTipAge = GetArg("-maxtipage", DEFAULT_MAX_TIP_AGE);
+    if (!mapMultiArgs["-bip9params"].empty()) {
+        // Allow overriding bip9 parameters for testing
+        if (!Params().MineBlocksOnDemand()) {
+            return InitError("BIP9 parameters may only be overridden on regtest.");
+        }
+        const vector<string>& deployments = mapMultiArgs["-bip9params"];
+        for (auto i : deployments) {
+            std::vector<std::string> vDeploymentParams;
+            boost::split(vDeploymentParams, i, boost::is_any_of(":"));
+            if (vDeploymentParams.size() != 3) {
+                return InitError("BIP9 parameters malformed, expecting deployment:start:end");
+            }
+            int64_t nStartTime, nTimeout;
+            if (!ParseInt64(vDeploymentParams[1], &nStartTime)) {
+                return InitError(strprintf("Invalid nStartTime (%s)", vDeploymentParams[1]));
+            }
+            if (!ParseInt64(vDeploymentParams[2], &nTimeout)) {
+                return InitError(strprintf("Invalid nTimeout (%s)", vDeploymentParams[2]));
+            }
+            bool found = false;
+            for (int i=0; i<(int)Consensus::MAX_VERSION_BITS_DEPLOYMENTS; ++i)
+            {
+                if (vDeploymentParams[0].compare(VersionBitsDeploymentInfo[i].name) == 0) {
+                    UpdateRegtestBIP9Parameters(Consensus::DeploymentPos(i), nStartTime, nTimeout);
+                    found = true;
+                    LogPrintf("Setting BIP9 activation parameters for %s to start=%ld, timeout=%ld\n", vDeploymentParams[0], nStartTime, nTimeout);
+                    break;
+                }
+            }
+            if (!found) {
+                return InitError(strprintf("Invalid deployment (%s)", vDeploymentParams[0]));
+            }
+        }
+    }
 
     // ********************************************************* Step 4: application initialization: dir lock, daemonize, pidfile, debug log