diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2278,15 +2278,28 @@
     // If this block is deactivating a fork, we move all mempool transactions
     // in front of disconnectpool for reprocessing in a future
     // updateMempoolForReorg call
-    if (pindexDelete->pprev != nullptr &&
-        GetNextBlockScriptFlags(consensusParams, pindexDelete) !=
-            GetNextBlockScriptFlags(consensusParams, pindexDelete->pprev)) {
-        LogPrint(BCLog::MEMPOOL,
-                 "Disconnecting mempool due to rewind of upgrade block\n");
-        if (disconnectpool) {
-            disconnectpool->importMempool(g_mempool);
+    if (pindexDelete->pprev != nullptr) {
+        bool changes = false;
+        changes |=
+            (GetNextBlockScriptFlags(consensusParams, pindexDelete) !=
+             GetNextBlockScriptFlags(consensusParams, pindexDelete->pprev));
+
+        changes |=
+            (GetDefaultAncestorLimit(consensusParams, pindexDelete) !=
+             GetDefaultAncestorLimit(consensusParams, pindexDelete->pprev));
+
+        changes |=
+            (GetDefaultDecendantLimit(consensusParams, pindexDelete) !=
+             GetDefaultDecendantLimit(consensusParams, pindexDelete->pprev));
+
+        if (changes) {
+            LogPrint(BCLog::MEMPOOL,
+                     "Disconnecting mempool due to rewind of upgrade block\n");
+            if (disconnectpool) {
+                disconnectpool->importMempool(g_mempool);
+            }
+            g_mempool.clear();
         }
-        g_mempool.clear();
     }
 
     if (disconnectpool) {
diff --git a/test/functional/abc-phonos-disconnectpool.py b/test/functional/abc-phonos-disconnectpool.py
new file mode 100755
--- /dev/null
+++ b/test/functional/abc-phonos-disconnectpool.py
@@ -0,0 +1,90 @@
+#!/usr/bin/env python3
+# Copyright (c) 2014-2019 The Bitcoin Core developers
+# Copyright (c) 2020 The Bitcoin developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+"""Test that long chains are trimmed from mempool on phonos-rollback"""
+
+from decimal import Decimal
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.txtools import pad_raw_tx
+from test_framework.util import (
+    assert_equal,
+    satoshi_round,
+)
+
+# Phonos dummy activation time
+ACTIVATION_TIME = 2000000000
+
+# Replay protection time needs to be moved beyond phonos activation
+REPLAY_PROTECTION_TIME = ACTIVATION_TIME * 2
+
+PREFORK_MAX_ANCESTORS = 25
+POSTFORK_MAX_ANCESTORS = 50
+
+
+class MempoolPhonosTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.num_nodes = 1
+
+        self.extra_args = [[
+            "-phononactivationtime={}".format(ACTIVATION_TIME),
+            "-replayprotectionactivationtime={}".format(
+                REPLAY_PROTECTION_TIME),
+            "-maxorphantx=1000"]]
+
+    def skip_test_if_missing_module(self):
+        self.skip_if_no_wallet()
+
+    # Build a transaction that spends parent_txid:vout
+    # Return amount sent
+    def chain_transaction(self, node, parent_txid, vout, value):
+        fee = Decimal(0.0001)
+        send_value = satoshi_round(value - fee)
+        inputs = [{'txid': parent_txid, 'vout': vout}]
+        outputs = {
+            node.getnewaddress(): send_value
+        }
+        rawtx = node.createrawtransaction(inputs, outputs)
+        signedtx = node.signrawtransactionwithwallet(rawtx)
+        txid = node.sendrawtransaction(pad_raw_tx(signedtx['hex']))
+        fulltx = node.getrawtransaction(txid, 1)
+        # make sure we didn't generate a change output
+        assert len(fulltx['vout']) == 1
+        return (txid, send_value)
+
+    def run_test(self):
+        # Mine some pre-fork blocks
+        node = self.nodes[0]
+        node.setmocktime(ACTIVATION_TIME - 10000)
+        node.generate(101)
+
+        pre_fork_height = node.getblockcount()
+
+        # Activate phonos
+        node.setmocktime(ACTIVATION_TIME)
+        self.nodes[0].generate(11)
+
+        # Mine a POSTFORK_MAX_ANCESTORS length chain
+        utxo = self.nodes[0].listunspent(1)[0]
+        txid = utxo['txid']
+        value = utxo['amount']
+
+        for i in range(POSTFORK_MAX_ANCESTORS):
+            (txid, sent_value) = self.chain_transaction(
+                self.nodes[0], txid, 0, value)
+            value = sent_value
+
+        assert_equal(len(node.getrawmempool(True)), POSTFORK_MAX_ANCESTORS)
+
+        # Rollback the fork
+        node.invalidateblock(node.getblockhash(pre_fork_height + 1))
+
+        # Assert that the mempool was trimmed to PREFORK_MAX_ANCESTORS
+        assert_equal(len(node.getrawmempool(True)), PREFORK_MAX_ANCESTORS)
+
+
+if __name__ == '__main__':
+    MempoolPhonosTest().main()