Index: src/test/java/quickfix/MessageTest.java
===================================================================
--- src/test/java/quickfix/MessageTest.java	(revision 740)
+++ src/test/java/quickfix/MessageTest.java	(working copy)
@@ -19,76 +19,22 @@
 
 package quickfix;
 
-import java.math.BigDecimal;
-import java.util.Calendar;
-import java.util.Date;
-import java.util.TimeZone;
-
 import junit.framework.TestCase;
-import quickfix.field.AllocAccount;
-import quickfix.field.AllocShares;
-import quickfix.field.AvgPx;
-import quickfix.field.BeginString;
-import quickfix.field.BidType;
-import quickfix.field.BodyLength;
-import quickfix.field.CheckSum;
-import quickfix.field.ClOrdID;
-import quickfix.field.CountryOfIssue;
-import quickfix.field.CrossID;
-import quickfix.field.CrossPrioritization;
-import quickfix.field.CrossType;
-import quickfix.field.CumQty;
-import quickfix.field.EncodedText;
-import quickfix.field.EncodedTextLen;
-import quickfix.field.EncryptMethod;
-import quickfix.field.ExecID;
-import quickfix.field.ExecType;
-import quickfix.field.HandlInst;
-import quickfix.field.Headline;
-import quickfix.field.IOIid;
-import quickfix.field.LeavesQty;
-import quickfix.field.ListID;
-import quickfix.field.ListSeqNo;
-import quickfix.field.MsgDirection;
-import quickfix.field.MsgSeqNum;
-import quickfix.field.MsgType;
-import quickfix.field.NoOrders;
-import quickfix.field.OrdStatus;
-import quickfix.field.OrdType;
-import quickfix.field.OrderID;
-import quickfix.field.OrderQty;
-import quickfix.field.PartyID;
-import quickfix.field.PartyIDSource;
-import quickfix.field.PartyRole;
-import quickfix.field.Price;
-import quickfix.field.RawData;
-import quickfix.field.RawDataLength;
-import quickfix.field.RefMsgType;
-import quickfix.field.SecureData;
-import quickfix.field.SecurityID;
-import quickfix.field.SecurityIDSource;
-import quickfix.field.SecurityType;
-import quickfix.field.SenderCompID;
-import quickfix.field.SendingTime;
-import quickfix.field.Side;
-import quickfix.field.Symbol;
-import quickfix.field.TargetCompID;
-import quickfix.field.TotNoOrders;
-import quickfix.field.TransactTime;
-import quickfix.field.UnderlyingCurrency;
-import quickfix.field.UnderlyingSymbol;
+import quickfix.field.*;
 import quickfix.fix42.NewOrderSingle;
 import quickfix.fix43.NewOrderList;
-import quickfix.fix44.ExecutionReport;
-import quickfix.fix44.IndicationOfInterest;
-import quickfix.fix44.Logon;
-import quickfix.fix44.NewOrderCross;
-import quickfix.fix44.News;
+import quickfix.fix44.*;
 import quickfix.fix44.Logon.NoMsgTypes;
 import quickfix.fix44.NewOrderSingle.NoPartyIDs;
 import quickfix.fix44.component.Instrument;
 import quickfix.fix44.component.Parties;
+import quickfix.util.ExpectedTestFailure;
 
+import java.math.BigDecimal;
+import java.util.Calendar;
+import java.util.Date;
+import java.util.TimeZone;
+
 public class MessageTest extends TestCase {
 
     public void testEmbeddedMessage() throws Exception {
@@ -183,6 +129,51 @@
     
     }
 
+    public void testDuplicateFieldsPresent() throws Exception {
+        final String data = "8=FIX.4.2\u00019=193\u000135=8\u000149=OPENFIX\u000156=MRKTC\u000152=20070919-21:28:11\u000134=101"+
+                            "\u000137=1190237122441-1\u000111=11902371224411\u000120=0\u000155=ORCL\u000154=1\u000138=2000"+
+                            "\u000140=2\u000144=13\u000117=1190237122441-2\u000132=0\u000131=0\u000114=0\u00016=0\u0001151=2000"+
+                            "\u000139=0\u0001150=0\u000138=2100\u000110=168\u0001";
+        final ExecutionReport executionReport = new ExecutionReport();
+        final DataDictionary dictionary = DataDictionaryTest.getDictionary();
+        assertNotNull(dictionary);
+        new ExpectedTestFailure(InvalidMessage.class, OrderQty.FIELD+"") {
+            protected void execute() throws Throwable {
+                executionReport.fromString(data, dictionary, true);
+            }
+        }.run();
+    }
+
+    public void testDuplicateTrailerFieldsPresent() throws Exception {
+        final String data = "8=FIX.4.2\u00019=193\u000135=8\u000149=OPENFIX\u000156=MRKTC\u000152=20070919-21:28:11\u000134=101"+
+                            "\u000137=1190237122441-1\u000111=11902371224411\u000120=0\u000155=ORCL\u000154=1\u000138=2000"+
+                            "\u000140=2\u000144=13\u000117=1190237122441-2\u000132=0\u000131=0\u000114=0\u00016=0\u0001151=2000"+
+                            "\u000139=0\u0001150=0\u000193=1\u000193=1\u000189=A\u000110=226\u0001";
+        final ExecutionReport executionReport = new ExecutionReport();
+        final DataDictionary dictionary = DataDictionaryTest.getDictionary();
+        assertNotNull(dictionary);
+        new ExpectedTestFailure(InvalidMessage.class, SignatureLength.FIELD+"") {
+            protected void execute() throws Throwable {
+                executionReport.fromString(data, dictionary, true);
+            }
+        }.run();
+    }
+
+    public void testDuplicateHeaderFieldsPresent() throws Exception {
+        final String data = "8=FIX.4.2\u00019=193\u000135=8\u000149=OPENFIX\u000156=MRKTC\u000149=OPENFIX\u000152=20070919-21:28:11\u000134=101"+
+                            "\u000137=1190237122441-1\u000111=11902371224411\u000120=0\u000155=ORCL\u000154=1\u000138=2000"+
+                            "\u000140=2\u000144=13\u000117=1190237122441-2\u000132=0\u000131=0\u000114=0\u00016=0\u0001151=2000"+
+                            "\u000139=0\u0001150=0\u000110=0\u0001";
+        final ExecutionReport executionReport = new ExecutionReport();
+        final DataDictionary dictionary = DataDictionaryTest.getDictionary();
+        assertNotNull(dictionary);
+        new ExpectedTestFailure(InvalidMessage.class, SenderCompID.FIELD+"") {
+            protected void execute() throws Throwable {
+                executionReport.fromString(data, dictionary, true);
+            }
+        }.run();
+    }
+
     public void testValidation() throws Exception {
         String data = "8=FIX.4.4
9=309
35=8
49=ASX
56=CL1_FIX44
34=4
52=20060324-01:05:58
"
                 + "17=X-B-WOW-1494E9A0:58BD3F9D-1109
150=D
39=0
11=184271
38=200
198=1494E9A0:58BD3F9D
"
Index: src/main/java/quickfix/Message.java
===================================================================
--- src/main/java/quickfix/Message.java	(revision 740)
+++ src/main/java/quickfix/Message.java	(working copy)
@@ -19,10 +19,10 @@
 
 package quickfix;
 
-import java.io.ByteArrayOutputStream;
-import java.text.DecimalFormat;
-import java.util.Iterator;
-import java.util.List;
+import org.w3c.dom.CDATASection;
+import org.w3c.dom.Document;
+import org.w3c.dom.Element;
+import quickfix.field.*;
 
 import javax.xml.parsers.DocumentBuilderFactory;
 import javax.xml.transform.OutputKeys;
@@ -30,41 +30,11 @@
 import javax.xml.transform.TransformerFactory;
 import javax.xml.transform.dom.DOMSource;
 import javax.xml.transform.stream.StreamResult;
+import java.io.ByteArrayOutputStream;
+import java.text.DecimalFormat;
+import java.util.Iterator;
+import java.util.List;
 
-import org.w3c.dom.CDATASection;
-import org.w3c.dom.Document;
-import org.w3c.dom.Element;
-
-import quickfix.field.BeginString;
-import quickfix.field.BodyLength;
-import quickfix.field.CheckSum;
-import quickfix.field.DeliverToCompID;
-import quickfix.field.DeliverToLocationID;
-import quickfix.field.DeliverToSubID;
-import quickfix.field.LastMsgSeqNumProcessed;
-import quickfix.field.MessageEncoding;
-import quickfix.field.MsgSeqNum;
-import quickfix.field.MsgType;
-import quickfix.field.OnBehalfOfCompID;
-import quickfix.field.OnBehalfOfLocationID;
-import quickfix.field.OnBehalfOfSendingTime;
-import quickfix.field.OnBehalfOfSubID;
-import quickfix.field.OrigSendingTime;
-import quickfix.field.PossDupFlag;
-import quickfix.field.PossResend;
-import quickfix.field.SecureDataLen;
-import quickfix.field.SenderCompID;
-import quickfix.field.SenderLocationID;
-import quickfix.field.SenderSubID;
-import quickfix.field.SendingTime;
-import quickfix.field.Signature;
-import quickfix.field.SignatureLength;
-import quickfix.field.TargetCompID;
-import quickfix.field.TargetLocationID;
-import quickfix.field.TargetSubID;
-import quickfix.field.XmlData;
-import quickfix.field.XmlDataLen;
-
 /**
  * Represents a FIX message.
  */
@@ -445,8 +415,6 @@
             }
         } catch (FieldNotFound e) {
             throw new InvalidMessage("Field not found: " + e.field);
-        } catch (InvalidMessage e) {
-            throw e;
         }
     }
 
@@ -481,7 +449,11 @@
 
         StringField field = extractField(dd, header);
         while (field != null && isHeaderField(field, dd)) {
-            header.setField(field);
+            if(!header.isSetField(field)) {
+                header.setField(field);
+            } else {
+                throw new InvalidMessage("Duplicate header field found: "+field.getField());
+            }
             field = extractField(dd, header);
         }
         pushBack(field);
@@ -511,7 +483,11 @@
                 }
                 header.setField(field);
             } else {
-                setField(field);
+                if(!isSetField(field)) {
+                    setField(field);
+                } else {
+                    throw new InvalidMessage("Duplicate field found: "+field.getField());
+                }
             }
             // Group case
             if (dd != null && dd.isGroup(getMsgType(), field.getField())) {
@@ -574,7 +550,11 @@
     private void parseTrailer(DataDictionary dd) throws InvalidMessage {
         StringField field = extractField(dd, trailer);
         while (field != null && isTrailerField(field, dd)) {
-            trailer.setField(field);
+            if(!trailer.isSetField(field)) {
+                trailer.setField(field);
+            } else {
+                throw new InvalidMessage("Duplicate trailer field found: "+field.getField());
+            }
             field = extractField(dd, trailer);
         }
     }