diff --git a/core/src/main/java/com/google/bitcoin/store/MemoryBlockStore.java b/core/src/main/java/com/google/bitcoin/store/MemoryBlockStore.java
index d97a287a..06539a41 100644
--- a/core/src/main/java/com/google/bitcoin/store/MemoryBlockStore.java
+++ b/core/src/main/java/com/google/bitcoin/store/MemoryBlockStore.java
@@ -18,18 +18,22 @@ package com.google.bitcoin.store;
 
 import com.google.bitcoin.core.*;
 
-import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.Map;
 
 /**
  * Keeps {@link com.google.bitcoin.core.StoredBlock}s in memory. Used primarily for unit testing.
  */
 public class MemoryBlockStore implements BlockStore {
-    private Map<Sha256Hash, StoredBlock> blockMap;
+    private LinkedHashMap<Sha256Hash, StoredBlock> blockMap = new LinkedHashMap<Sha256Hash, StoredBlock>() {
+        @Override
+        protected boolean removeEldestEntry(Map.Entry<Sha256Hash, StoredBlock> eldest) {
+            return blockMap.size() > 5000;
+        }
+    };
     private StoredBlock chainHead;
 
     public MemoryBlockStore(NetworkParameters params) {
-        blockMap = new HashMap<Sha256Hash, StoredBlock>();
         // Insert the genesis block.
         try {
             Block genesisHeader = params.getGenesisBlock().cloneAsHeader();