diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index ecba5ca3e2c..6d2920ece51 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -1411,6 +1411,7 @@ util::Result<std::pair<std::vector<FeeFrac>, std::vector<FeeFrac>>> CTxMemPool::
 
 CTxMemPool::ChangeSet::TxHandle CTxMemPool::ChangeSet::StageAddition(const CTransactionRef& tx, const CAmount fee, int64_t time, unsigned int entry_height, uint64_t entry_sequence, bool spends_coinbase, int64_t sigops_cost, LockPoints lp)
 {
+    Assume(m_to_add.find(tx->GetHash()) == m_to_add.end());
     auto newit = m_to_add.emplace(tx, fee, time, entry_height, entry_sequence, spends_coinbase, sigops_cost, lp).first;
     m_entry_vec.push_back(newit);
     return newit;