diff --git a/src/main.cpp b/src/main.cpp
index 10062c915..9d881f42a 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -2072,6 +2072,12 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
 
         {
             LOCK(pool.cs);
+            // Bound mempool memory: this fork never ported fee-ordered TrimToSize eviction, so
+            // instead of evicting we refuse new admissions once the pool exceeds -maxmempool.
+            // removeExpired() already clears unmineable expired txs on each block connect; this
+            // caps the total footprint against a flood of otherwise-minable/low-fee txs (OOM DoS).
+            if ( pool.DynamicMemoryUsage() > (size_t)GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000 )
+                return state.DoS(0, error("AcceptToMemoryPool: mempool full, rejecting tx %s", hash.ToString()), REJECT_INSUFFICIENTFEE, "mempool-full");
             // Store transaction in memory
             pool.addUnchecked(hash, entry, !IsInitialBlockDownload());
 
diff --git a/src/main.h b/src/main.h
index 26689de83..6ecef2f77 100644
--- a/src/main.h
+++ b/src/main.h
@@ -66,6 +66,8 @@ class PrecomputedTransactionData;
 
 struct CNodeStateStats;
 #define DEFAULT_MEMPOOL_EXPIRY 1
+/** Default for -maxmempool, maximum megabytes of mempool memory usage */
+#define DEFAULT_MAX_MEMPOOL_SIZE 300
 #define _COINBASE_MATURITY 100
 
 /** Default for -blockmaxsize and -blockminsize, which control the range of sizes the mining code will create **/