diff --git a/src/chainparams.cpp b/src/chainparams.cpp
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -136,6 +136,9 @@
         // Nov 15, 2020 12:00:00 UTC protocol upgrade
         consensus.axionActivationTime = 1605441600;
 
+        // May 15, 2021 12:00:00 UTC protocol upgrade
+        consensus.tachyonActivationTime = 1621080000;
+
         /**
          * The message start string is designed to be unlikely to occur in
          * normal data. The characters are rarely used upper ASCII, not valid as
@@ -331,6 +334,9 @@
         // Nov 15, 2020 12:00:00 UTC protocol upgrade
         consensus.axionActivationTime = 1605441600;
 
+        // May 15, 2021 12:00:00 UTC protocol upgrade
+        consensus.tachyonActivationTime = 1621080000;
+
         diskMagic[0] = 0x0b;
         diskMagic[1] = 0x11;
         diskMagic[2] = 0x09;
@@ -475,6 +481,9 @@
         // Nov 15, 2020 12:00:00 UTC protocol upgrade
         consensus.axionActivationTime = 1605441600;
 
+        // May 15, 2021 12:00:00 UTC protocol upgrade
+        consensus.tachyonActivationTime = 1621080000;
+
         diskMagic[0] = 0xfa;
         diskMagic[1] = 0xbf;
         diskMagic[2] = 0xb5;
diff --git a/src/consensus/params.h b/src/consensus/params.h
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -82,6 +82,8 @@
     int phononActivationTime;
     /** Unix time used for MTP activation of 15 Nov 2020 12:00:00 UTC upgrade */
     int axionActivationTime;
+    /** Unix time used for MTP activation of 15 May 2021 12:00:00 UTC upgrade */
+    int tachyonActivationTime;
 
     /**
      * Don't warn about unknown BIP 9 activations below this height.
diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -277,7 +277,7 @@
 static bool IsReplayProtectionEnabled(const Consensus::Params &params,
                                       int64_t nMedianTimePast) {
     return nMedianTimePast >= gArgs.GetArg("-replayprotectionactivationtime",
-                                           params.axionActivationTime);
+                                           params.tachyonActivationTime);
 }
 
 static bool IsReplayProtectionEnabled(const Consensus::Params &params,