diff --git a/core/pom.xml b/core/pom.xml
index 0b395c84..93d585aa 100644
--- a/core/pom.xml
+++ b/core/pom.xml
@@ -218,6 +218,11 @@
             <groupId>com.google.protobuf</groupId>
             <artifactId>protobuf-java</artifactId>
         </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava-base</artifactId>
+            <version>r03</version>
+        </dependency>
     </dependencies>
 
 </project>
\ No newline at end of file
diff --git a/core/src/main/java/com/google/bitcoin/core/Block.java b/core/src/main/java/com/google/bitcoin/core/Block.java
index e906cd42..6677d070 100644
--- a/core/src/main/java/com/google/bitcoin/core/Block.java
+++ b/core/src/main/java/com/google/bitcoin/core/Block.java
@@ -16,6 +16,7 @@
 
 package com.google.bitcoin.core;
 
+import com.google.common.base.Preconditions;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -87,9 +88,9 @@ public class Block extends Message {
         length = 80;
     }
 
-	/** Constructs a block object from the BitCoin wire format. */
+	/** Constructs a block object from the Bitcoin wire format. */
     public Block(NetworkParameters params, byte[] payloadBytes) throws ProtocolException {
-        super(params, payloadBytes, 0);
+        super(params, payloadBytes, 0, false, false, payloadBytes.length);
     }
 
     /**
@@ -170,8 +171,9 @@ public class Block extends Message {
         // Ignore the header since it has fixed length. If length is not provided we will have to
         // invoke a light parse of transactions to calculate the length.
         if (length == UNKNOWN_LENGTH) {
-            assert !parseLazy : "Performing lite parse of block transaction as block was initialised from byte array " +
-                    "without providing length.  This should never need to happen. parseLazy: " + parseLazy;
+            Preconditions.checkState(parseLazy,
+                    "Performing lite parse of block transaction as block was initialised from byte array " +
+                    "without providing length.  This should never need to happen.");
             parseTransactions();
             length = cursor - offset;
         } else {
@@ -334,7 +336,7 @@ public class Block extends Message {
 
         // we have completely cached byte array.
         if (headerBytesValid && transactionBytesValid) {
-            assert bytes != null : "Bytes should never be null if headerBytesValid && transactionBytesValid";
+            Preconditions.checkNotNull(bytes, "Bytes should never be null if headerBytesValid && transactionBytesValid");
             if (length == bytes.length) {
                 return bytes;
             } else {
@@ -674,7 +676,7 @@ public class Block extends Message {
         // an invalid block, but if we didn't validate this then an untrusted man-in-the-middle could obtain the next
         // valid block from the network and simply replace the transactions in it with their own fictional
         // transactions that reference spent or non-existant inputs.
-        assert transactions.size() > 0;
+        Preconditions.checkState(!transactions.isEmpty());
         maybeParseTransactions();
         checkTransactions();
         checkMerkleRoot();
diff --git a/core/src/main/java/com/google/bitcoin/core/Peer.java b/core/src/main/java/com/google/bitcoin/core/Peer.java
index c9a55b0f..3e815e6d 100644
--- a/core/src/main/java/com/google/bitcoin/core/Peer.java
+++ b/core/src/main/java/com/google/bitcoin/core/Peer.java
@@ -19,6 +19,7 @@ package com.google.bitcoin.core;
 import com.google.bitcoin.store.BlockStore;
 import com.google.bitcoin.store.BlockStoreException;
 import com.google.bitcoin.utils.EventListenerInvoker;
+import com.google.common.base.Preconditions;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -255,11 +256,12 @@ public class Peer {
     private void processHeaders(HeadersMessage m) throws IOException, ProtocolException {
         // Runs in network loop thread for this peer.
         //
-        // This can happen if a peer just randomly sends us a "headers" message (should never happen), or more likely
-        // when we've requested them as part of chain download using fast catchup. We need to add each block to the
-        // chain if it pre-dates the fast catchup time. If we go past it, we can stop processing the headers and request
-        // the full blocks from that point on instead.
-        assert !downloadBlockBodies;
+        // This method can run if a peer just randomly sends us a "headers" message (should never happen), or more
+        // likely when we've requested them as part of chain download using fast catchup. We need to add each block to
+        // the chain if it pre-dates the fast catchup time. If we go past it, we can stop processing the headers and
+        // request the full blocks from that point on instead.
+        Preconditions.checkState(!downloadBlockBodies);
+
         try {
             for (int i = 0; i < m.getBlockHeaders().size(); i++) {
                 Block header = m.getBlockHeaders().get(i);
@@ -446,7 +448,7 @@ public class Peer {
         synchronized (announcedTransactionHashes) {
             if (announcedTransactionHashes.containsKey(tx.getHash())) {
                 Transaction storedTx = announcedTransactionHashes.get(tx.getHash());
-                assert storedTx == tx || storedTx == null : "single Transaction instance";
+                Preconditions.checkState(storedTx == tx || storedTx == null, "single Transaction instance");
                 log.debug("Provided with a downloaded transaction we have seen before: {}", tx.getHash());
                 tx.getConfidence().markBroadcastBy(address);
             } else {
@@ -553,15 +555,13 @@ public class Peer {
 
         public T get() throws InterruptedException, ExecutionException {
             latch.await();
-            assert result != null;
-            return result;
+            return Preconditions.checkNotNull(result);
         }
 
         public T get(long l, TimeUnit timeUnit) throws InterruptedException, ExecutionException, TimeoutException {
             if (!latch.await(l, timeUnit))
                 throw new TimeoutException();
-            assert result != null;
-            return result;
+            return Preconditions.checkNotNull(result);
         }
 
         InventoryItem getItem() {
@@ -686,12 +686,10 @@ public class Peer {
     public int getPeerBlockHeightDifference() {
         // Chain will overflow signed int blocks in ~41,000 years.
         int chainHeight = (int) conn.getVersionMessage().bestHeight;
-        if (chainHeight <= 0) {
-            // This should not happen because we shouldn't have given the user a Peer that is to another client-mode
-            // node, nor should it be unconnected. If that happens it means the user overrode us somewhere or there is
-            // a bug in the peer management code.
-            throw new RuntimeException("Connected to peer advertising zero/negative chain height.");
-        }
+        // chainHeight should not be zero/negative because we shouldn't have given the user a Peer that is to another
+        // client-mode node, nor should it be unconnected. If that happens it means the user overrode us somewhere or
+        // there is a bug in the peer management code.
+        Preconditions.checkState(chainHeight > 0, "Connected to peer with zero/negative chain height", chainHeight);
         return chainHeight - blockChain.getChainHead().getHeight();
     }
 
diff --git a/core/src/test/java/com/google/bitcoin/core/BitcoinSerializerTest.java b/core/src/test/java/com/google/bitcoin/core/BitcoinSerializerTest.java
index fc4c70c9..22336c67 100644
--- a/core/src/test/java/com/google/bitcoin/core/BitcoinSerializerTest.java
+++ b/core/src/test/java/com/google/bitcoin/core/BitcoinSerializerTest.java
@@ -203,7 +203,6 @@ public class BitcoinSerializerTest {
      */
     @Test
     public void testHeaders1() throws Exception {
-
         BitcoinSerializer bs = new BitcoinSerializer(NetworkParameters.prodNet(), true,
                 null);