diff --git a/src/chainparams.cpp b/src/chainparams.cpp
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -128,8 +128,8 @@
         // November 13, 2017 hard fork
         consensus.daaHeight = 504031;
 
-        // Nov 15, 2018 hard fork
-        consensus.magneticAnomalyActivationTime = 1542300000;
+        // November 15, 2018 hard fork
+        consensus.magneticAnomalyHeight = 556766;
 
         // Wed, 15 May 2019 12:00:00 UTC hard fork
         consensus.greatWallActivationTime = 1557921600;
@@ -299,8 +299,8 @@
         // November 13, 2017 hard fork
         consensus.daaHeight = 1188697;
 
-        // Nov 15, 2018 hard fork
-        consensus.magneticAnomalyActivationTime = 1542300000;
+        // November 15, 2018 hard fork
+        consensus.magneticAnomalyHeight = 1267996;
 
         // Wed, 15 May 2019 12:00:00 UTC hard fork
         consensus.greatWallActivationTime = 1557921600;
@@ -419,8 +419,8 @@
         // November 13, 2017 hard fork is always on on regtest.
         consensus.daaHeight = 0;
 
-        // Nov 15, 2018 hard fork
-        consensus.magneticAnomalyActivationTime = 1542300000;
+        // November 15, 2018 hard fork is always on on regtest.
+        consensus.magneticAnomalyHeight = 0;
 
         // Wed, 15 May 2019 12:00:00 UTC hard fork
         consensus.greatWallActivationTime = 1557921600;
diff --git a/src/consensus/activation.h b/src/consensus/activation.h
--- a/src/consensus/activation.h
+++ b/src/consensus/activation.h
@@ -16,13 +16,10 @@
 /** Check if DAA HF has activated. */
 bool IsDAAEnabled(const Config &config, const CBlockIndex *pindexPrev);
 
-/** Check if Nov 15, 2018 HF has activated. */
+/** Check if Nov 15, 2018 HF has activated using block height. */
+bool IsMagneticAnomalyEnabled(const Config &config, int32_t nHeight);
+/** Check if Nov 15, 2018 HF has activated using previous block index. */
 bool IsMagneticAnomalyEnabled(const Config &config,
                               const CBlockIndex *pindexPrev);
-/**
- * Also check if Nov 15, 2018 HF has activated, but with an API that isn't as
- * safe.
- */
-bool IsMagneticAnomalyEnabled(const Config &config, int64_t nMedianTimePast);
 
 #endif // BITCOIN_CONSENSUS_ACTIVATION_H
diff --git a/src/consensus/activation.cpp b/src/consensus/activation.cpp
--- a/src/consensus/activation.cpp
+++ b/src/consensus/activation.cpp
@@ -33,11 +33,9 @@
     return IsDAAEnabled(config, pindexPrev->nHeight);
 }
 
-bool IsMagneticAnomalyEnabled(const Config &config, int64_t nMedianTimePast) {
-    return nMedianTimePast >= gArgs.GetArg("-magneticanomalyactivationtime",
-                                           config.GetChainParams()
-                                               .GetConsensus()
-                                               .magneticAnomalyActivationTime);
+bool IsMagneticAnomalyEnabled(const Config &config, int32_t nHeight) {
+    return nHeight >=
+           config.GetChainParams().GetConsensus().magneticAnomalyHeight;
 }
 
 bool IsMagneticAnomalyEnabled(const Config &config,
@@ -46,5 +44,5 @@
         return false;
     }
 
-    return IsMagneticAnomalyEnabled(config, pindexPrev->GetMedianTimePast());
+    return IsMagneticAnomalyEnabled(config, pindexPrev->nHeight);
 }
diff --git a/src/consensus/params.h b/src/consensus/params.h
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -54,8 +54,8 @@
     int uahfHeight;
     /** Block height at which the new DAA becomes active */
     int daaHeight;
-    /** Unix time used for MTP activation of Nov 15 2018, hardfork */
-    int magneticAnomalyActivationTime;
+    /** Block height at which the magnetic anomaly activation becomes active */
+    int magneticAnomalyHeight;
     /** Unix time used for MTP activation of 15 May 2019 12:00:00 UTC upgrade */
     int greatWallActivationTime;
     /**
diff --git a/src/consensus/tx_verify.cpp b/src/consensus/tx_verify.cpp
--- a/src/consensus/tx_verify.cpp
+++ b/src/consensus/tx_verify.cpp
@@ -46,7 +46,7 @@
                          "non-final transaction");
     }
 
-    if (IsMagneticAnomalyEnabled(config, nMedianTimePast)) {
+    if (IsMagneticAnomalyEnabled(config, nHeight)) {
         // Size limit
         if (::GetSerializeSize(tx, SER_NETWORK, PROTOCOL_VERSION) <
             MIN_TX_SIZE) {
diff --git a/src/test/transaction_tests.cpp b/src/test/transaction_tests.cpp
--- a/src/test/transaction_tests.cpp
+++ b/src/test/transaction_tests.cpp
@@ -775,17 +775,17 @@
 
 BOOST_AUTO_TEST_CASE(txsize_activation_test) {
     const Config &config = GetConfig();
-    const int64_t magneticAnomalyActivationTime =
-        config.GetChainParams().GetConsensus().magneticAnomalyActivationTime;
+    const int32_t magneticAnomalyActivationHeight =
+        config.GetChainParams().GetConsensus().magneticAnomalyHeight;
 
     // A minimaly sized transction.
     CTransaction minTx;
     CValidationState state;
 
-    BOOST_CHECK(ContextualCheckTransaction(config, minTx, state, 1234, 5678,
-                                           magneticAnomalyActivationTime - 1));
-    BOOST_CHECK(!ContextualCheckTransaction(config, minTx, state, 1234, 5678,
-                                            magneticAnomalyActivationTime));
+    BOOST_CHECK(ContextualCheckTransaction(
+        config, minTx, state, magneticAnomalyActivationHeight - 1, 5678, 1234));
+    BOOST_CHECK(!ContextualCheckTransaction(
+        config, minTx, state, magneticAnomalyActivationHeight, 5678, 1234));
     BOOST_CHECK_EQUAL(state.GetRejectCode(), REJECT_INVALID);
     BOOST_CHECK_EQUAL(state.GetRejectReason(), "bad-txns-undersize");
 }