diff --git a/src/main/java/com/corundumstudio/socketio/parser/Encoder.java b/src/main/java/com/corundumstudio/socketio/parser/Encoder.java
index 58189ac..8788b53 100644
--- a/src/main/java/com/corundumstudio/socketio/parser/Encoder.java
+++ b/src/main/java/com/corundumstudio/socketio/parser/Encoder.java
@@ -41,7 +41,7 @@ public class Encoder {
 		int type = packet.getType().getValue();
 		String id = packet.getId();
 		String endpoint = packet.getEndpoint();
-		String ack = packet.getAck();
+		Object ack = packet.getAck();
 		Object data = packet.getData();
 		
 		switch(packet.getType()) {
@@ -83,16 +83,16 @@ public class Encoder {
 					adviceCode = packet.getAdvice().getValue();
 				}
 				
-				StringBuilder errorData = new StringBuilder();
 				if (reasonCode != -1 || adviceCode != -1) {
+					StringBuilder errorData = new StringBuilder();
 					if (reasonCode != -1) {
 						errorData.append(reasonCode);
 					}
 					if (adviceCode != -1) {
 						errorData.append("+").append(adviceCode);
 					}
+					data = errorData;
 				}
-				data = errorData;
 				break;
 				
 		}
diff --git a/src/test/java/com/corundumstudio/socketio/parser/EncoderErrorPacketTest.java b/src/test/java/com/corundumstudio/socketio/parser/EncoderErrorPacketTest.java
new file mode 100644
index 0000000..92d51c9
--- /dev/null
+++ b/src/test/java/com/corundumstudio/socketio/parser/EncoderErrorPacketTest.java
@@ -0,0 +1,44 @@
+package com.corundumstudio.socketio.parser;
+
+import java.io.IOException;
+
+import org.codehaus.jackson.map.ObjectMapper;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class EncoderErrorPacketTest {
+
+	private Encoder encoder = new Encoder(new ObjectMapper());
+	
+	@Test
+	public void testEncode() throws IOException {
+		Packet packet = new Packet(PacketType.ERROR);
+		String result = encoder.encodePacket(packet);
+		Assert.assertEquals("7::", result);
+	}
+	
+	@Test
+	public void testEncodeWithReason() throws IOException {
+		Packet packet = new Packet(PacketType.ERROR);
+		packet.setReason(ErrorReason.TRANSPORT_NOT_SUPPORTED);
+		String result = encoder.encodePacket(packet);
+		Assert.assertEquals("7:::0", result);
+	}
+
+	@Test
+	public void testEncodeWithReasonAndAdvice() throws IOException {
+		Packet packet = new Packet(PacketType.ERROR);
+		packet.setReason(ErrorReason.UNAUTHORIZED);
+		packet.setAdvice(ErrorAdvice.RECONNECT);
+		String result = encoder.encodePacket(packet);
+		Assert.assertEquals("7:::2+0", result);
+	}
+
+	@Test
+	public void testEncodeWithEndpoint() throws IOException {
+		Packet packet = new Packet(PacketType.ERROR);
+		packet.setEndpoint("/woot");
+		String result = encoder.encodePacket(packet);
+		Assert.assertEquals("7::/woot", result);
+	}
+}