diff --git a/bramble-core/src/main/java/org/briarproject/bramble/sync/SyncRecordReaderImpl.java b/bramble-core/src/main/java/org/briarproject/bramble/sync/SyncRecordReaderImpl.java
index 2329999ce..250f72953 100644
--- a/bramble-core/src/main/java/org/briarproject/bramble/sync/SyncRecordReaderImpl.java
+++ b/bramble-core/src/main/java/org/briarproject/bramble/sync/SyncRecordReaderImpl.java
@@ -30,6 +30,7 @@ import static org.briarproject.bramble.api.sync.RecordTypes.OFFER;
 import static org.briarproject.bramble.api.sync.RecordTypes.PRIORITY;
 import static org.briarproject.bramble.api.sync.RecordTypes.REQUEST;
 import static org.briarproject.bramble.api.sync.RecordTypes.VERSIONS;
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_SUPPORTED_VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.PRIORITY_NONCE_BYTES;
@@ -126,6 +127,8 @@ class SyncRecordReaderImpl implements SyncRecordReader {
 		byte[] payload = nextRecord.getPayload();
 		if (payload.length <= MESSAGE_HEADER_LENGTH)
 			throw new FormatException();
+		if (payload.length > MAX_MESSAGE_LENGTH)
+			throw new FormatException();
 		// Validate timestamp
 		long timestamp = ByteUtils.readUint64(payload, UniqueId.LENGTH);
 		if (timestamp < 0) throw new FormatException();
diff --git a/bramble-core/src/test/java/org/briarproject/bramble/sync/SyncRecordReaderImplTest.java b/bramble-core/src/test/java/org/briarproject/bramble/sync/SyncRecordReaderImplTest.java
index 2c6b0002b..d4eb61ff5 100644
--- a/bramble-core/src/test/java/org/briarproject/bramble/sync/SyncRecordReaderImplTest.java
+++ b/bramble-core/src/test/java/org/briarproject/bramble/sync/SyncRecordReaderImplTest.java
@@ -6,13 +6,18 @@ import org.briarproject.bramble.api.UniqueId;
 import org.briarproject.bramble.api.record.Record;
 import org.briarproject.bramble.api.record.RecordReader;
 import org.briarproject.bramble.api.sync.Ack;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
+import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.Offer;
 import org.briarproject.bramble.api.sync.Priority;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
 import org.briarproject.bramble.api.sync.Versions;
 import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.briarproject.bramble.test.PredicateMatcher;
+import org.hamcrest.Matcher;
 import org.jmock.Expectations;
 import org.junit.Test;
 
@@ -23,12 +28,15 @@ import javax.annotation.Nullable;
 
 import static org.briarproject.bramble.api.record.Record.MAX_RECORD_PAYLOAD_BYTES;
 import static org.briarproject.bramble.api.sync.RecordTypes.ACK;
+import static org.briarproject.bramble.api.sync.RecordTypes.MESSAGE;
 import static org.briarproject.bramble.api.sync.RecordTypes.OFFER;
 import static org.briarproject.bramble.api.sync.RecordTypes.PRIORITY;
 import static org.briarproject.bramble.api.sync.RecordTypes.REQUEST;
 import static org.briarproject.bramble.api.sync.RecordTypes.VERSIONS;
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_IDS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_SUPPORTED_VERSIONS;
+import static org.briarproject.bramble.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.PRIORITY_NONCE_BYTES;
 import static org.briarproject.bramble.api.sync.SyncConstants.PROTOCOL_VERSION;
 import static org.briarproject.bramble.test.TestUtils.getRandomBytes;
@@ -46,6 +54,38 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 	private final SyncRecordReader reader =
 			new SyncRecordReaderImpl(messageFactory, recordReader);
 
+	@Test
+	public void testNoFormatExceptionIfMessageIsMinimumSize() throws Exception {
+		expectReadRecord(createMessage(MESSAGE_HEADER_LENGTH + 1));
+		expectCreateMessage(1);
+
+		reader.readMessage();
+	}
+
+	@Test(expected = FormatException.class)
+	public void testFormatExceptionIfMessageIsTooSmall() throws Exception {
+		expectReadRecord(createMessage(MESSAGE_HEADER_LENGTH));
+
+		reader.readMessage();
+	}
+
+	@Test
+	public void testNoFormatExceptionIfMessageIsMaximumSize() throws Exception {
+		expectReadRecord(createMessage(MESSAGE_HEADER_LENGTH
+				+ MAX_MESSAGE_BODY_LENGTH));
+		expectCreateMessage(MAX_MESSAGE_BODY_LENGTH);
+
+		reader.readMessage();
+	}
+
+	@Test(expected = FormatException.class)
+	public void testFormatExceptionIfMessageIsTooLarge() throws Exception {
+		expectReadRecord(createMessage(MESSAGE_HEADER_LENGTH
+				+ MAX_MESSAGE_BODY_LENGTH + 1));
+
+		reader.readMessage();
+	}
+
 	@Test
 	public void testNoFormatExceptionIfAckIsMaximumSize() throws Exception {
 		expectReadRecord(createAck());
@@ -158,6 +198,20 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 		assertTrue(reader.eof());
 	}
 
+	private void expectCreateMessage(int bodyLength) {
+		MessageId messageId = new MessageId(getRandomId());
+		GroupId groupId = new GroupId(getRandomId());
+		long timestamp = System.currentTimeMillis();
+
+		context.checking(new Expectations() {{
+			Matcher<byte[]> matcher = new PredicateMatcher<>(byte[].class,
+					b -> b.length == MESSAGE_HEADER_LENGTH + bodyLength);
+			oneOf(messageFactory).createMessage(with(matcher));
+			will(returnValue(new Message(messageId, groupId, timestamp,
+					new byte[bodyLength])));
+		}});
+	}
+
 	private void expectReadRecord(@Nullable Record record) throws Exception {
 		context.checking(new Expectations() {{
 			//noinspection unchecked
@@ -167,6 +221,10 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 		}});
 	}
 
+	private Record createMessage(int payloadLength) {
+		return new Record(PROTOCOL_VERSION, MESSAGE, new byte[payloadLength]);
+	}
+
 	private Record createAck() throws Exception {
 		return new Record(PROTOCOL_VERSION, ACK, createPayload());
 	}