diff --git a/CHANGES.txt b/CHANGES.txt
index 6e802c8b6..ba8d15efb 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -5,6 +5,8 @@ November 18, 2012
 * fixed: undefined rule refs caused exception
 * cleanup, rm dead etypes, add check for ids that cause code gen issues
 * added notion of one-off error
+* added check for v3 backward incompatibilities:
+** tree grammars
 
 November 17, 2012
 
diff --git a/tool/src/org/antlr/v4/Tool.java b/tool/src/org/antlr/v4/Tool.java
index d7efcaf20..82df03793 100644
--- a/tool/src/org/antlr/v4/Tool.java
+++ b/tool/src/org/antlr/v4/Tool.java
@@ -46,6 +46,7 @@ import org.antlr.v4.parse.ANTLRParser;
 import org.antlr.v4.parse.GrammarASTAdaptor;
 import org.antlr.v4.parse.GrammarTreeVisitor;
 import org.antlr.v4.parse.ToolANTLRParser;
+import org.antlr.v4.parse.v3TreeGrammarException;
 import org.antlr.v4.runtime.misc.LogManager;
 import org.antlr.v4.runtime.misc.Nullable;
 import org.antlr.v4.semantics.SemanticPipeline;
@@ -556,7 +557,7 @@ public class Tool {
 			}
 
 			ANTLRFileStream in = new ANTLRFileStream(file.getAbsolutePath(), grammarEncoding);
-			GrammarRootAST t = load(in);
+			GrammarRootAST t = load(fileName, in);
 			return t;
 		}
 		catch (IOException ioe) {
@@ -586,17 +587,17 @@ public class Tool {
 		}
 
 		ANTLRFileStream in = new ANTLRFileStream(importedFile.getAbsolutePath());
-		GrammarRootAST root = load(in);
+		GrammarRootAST root = load(g.fileName, in);
 		Grammar imported = createGrammar(root);
 		imported.fileName = importedFile.getAbsolutePath();
 		return imported;
 	}
 
 	public GrammarRootAST loadFromString(String grammar) {
-		return load(new ANTLRStringStream(grammar));
+		return load("<string>", new ANTLRStringStream(grammar));
 	}
 
-	public GrammarRootAST load(CharStream in) {
+	public GrammarRootAST load(String fileName, CharStream in) {
 		try {
 			GrammarASTAdaptor adaptor = new GrammarASTAdaptor(in);
 			ANTLRLexer lexer = new ANTLRLexer(in);
@@ -604,15 +605,20 @@ public class Tool {
 			lexer.tokens = tokens;
 			ToolANTLRParser p = new ToolANTLRParser(tokens, this);
 			p.setTreeAdaptor(adaptor);
-			ParserRuleReturnScope r = p.grammarSpec();
-			GrammarAST root = (GrammarAST)r.getTree();
-			if ( root instanceof GrammarRootAST) {
-				((GrammarRootAST)root).hasErrors = p.getNumberOfSyntaxErrors()>0;
-				((GrammarRootAST)root).tokens = tokens;
-				if ( grammarOptions!=null ) {
-					((GrammarRootAST)root).cmdLineOptions = grammarOptions;
+			try {
+				ParserRuleReturnScope r = p.grammarSpec();
+				GrammarAST root = (GrammarAST)r.getTree();
+				if ( root instanceof GrammarRootAST) {
+					((GrammarRootAST)root).hasErrors = p.getNumberOfSyntaxErrors()>0;
+					((GrammarRootAST)root).tokens = tokens;
+					if ( grammarOptions!=null ) {
+						((GrammarRootAST)root).cmdLineOptions = grammarOptions;
+					}
+					return ((GrammarRootAST)root);
 				}
-				return ((GrammarRootAST)root);
+			}
+			catch (v3TreeGrammarException e) {
+				errMgr.grammarError(ErrorType.V3_TREE_GRAMMAR, fileName, e.location);
 			}
 			return null;
 		}
diff --git a/tool/src/org/antlr/v4/parse/ANTLRLexer.g b/tool/src/org/antlr/v4/parse/ANTLRLexer.g
index b289f21e2..be707ec2f 100644
--- a/tool/src/org/antlr/v4/parse/ANTLRLexer.g
+++ b/tool/src/org/antlr/v4/parse/ANTLRLexer.g
@@ -398,6 +398,7 @@ FRAGMENT     : 'fragment'             ;
 LEXER        : 'lexer'                ;
 PARSER       : 'parser'               ;
 GRAMMAR      : 'grammar'              ;
+TREE_GRAMMAR : 'tree' WSNLCHARS* 'grammar' ;
 PROTECTED    : 'protected'            ;
 PUBLIC       : 'public'               ;
 PRIVATE      : 'private'              ;
diff --git a/tool/src/org/antlr/v4/parse/ANTLRParser.g b/tool/src/org/antlr/v4/parse/ANTLRParser.g
index cf0b6b099..36eebcb78 100644
--- a/tool/src/org/antlr/v4/parse/ANTLRParser.g
+++ b/tool/src/org/antlr/v4/parse/ANTLRParser.g
@@ -1,6 +1,6 @@
 /*
  [The "BSD license"]
- Copyright (c) 2010 Jim Idle, Terence Parr
+ Copyright (c) 2012 Jim Idle, Terence Parr
  All rights reserved.
 
  Redistribution and use in source and binary forms, with or without
@@ -99,7 +99,7 @@ tokens {
 @header {
 /*
  [The "BSD licence"]
- Copyright (c) 2005-2009 Terence Parr
+ Copyright (c) 2005-20012 Terence Parr
  All rights reserved.
 
  Redistribution and use in source and binary forms, with or without
@@ -202,6 +202,7 @@ if ( options!=null ) {
 
 grammarType
 @after {
+	if ( $tg!=null ) throw new v3TreeGrammarException(tg);
 	if ( $t!=null ) ((GrammarRootAST)$tree).grammarType = $t.type;
 	else ((GrammarRootAST)$tree).grammarType=COMBINED;
 }
@@ -211,6 +212,8 @@ grammarType
 
 		// A combined lexer and parser specification
 		| 	g=GRAMMAR          -> GRAMMAR<GrammarRootAST>[$g, "COMBINED_GRAMMAR"]
+		|   tg=TREE_GRAMMAR
+			
 		)
     ;
 
diff --git a/tool/src/org/antlr/v4/parse/v3TreeGrammarException.java b/tool/src/org/antlr/v4/parse/v3TreeGrammarException.java
new file mode 100644
index 000000000..e0f407b41
--- /dev/null
+++ b/tool/src/org/antlr/v4/parse/v3TreeGrammarException.java
@@ -0,0 +1,12 @@
+package org.antlr.v4.parse;
+
+import org.antlr.runtime.Token;
+import org.antlr.v4.runtime.misc.ParseCancellationException;
+
+public class v3TreeGrammarException extends ParseCancellationException {
+	public Token location;
+
+	public v3TreeGrammarException(Token location) {
+		this.location = location;
+	}
+}
diff --git a/tool/src/org/antlr/v4/tool/ErrorType.java b/tool/src/org/antlr/v4/tool/ErrorType.java
index 5ba7e4c52..b6c632f47 100644
--- a/tool/src/org/antlr/v4/tool/ErrorType.java
+++ b/tool/src/org/antlr/v4/tool/ErrorType.java
@@ -116,6 +116,9 @@ public enum ErrorType {
 	LEXER_COMMAND_PLACEMENT_ISSUE(133, "->command in lexer rule <arg> must be last element of single outermost alt", ErrorSeverity.ERROR),
 	USE_OF_BAD_WORD(134, "symbol <arg> conflicts with generated code in target language or runtime", ErrorSeverity.ERROR),
 
+	// Backward incompatibility errors
+	V3_TREE_GRAMMAR(200, "tree grammars are not supported in ANTLR v4", ErrorSeverity.ERROR_ONE_OFF),
+
     // Dependency sorting errors
 
     /** t1.g4 -> t2.g4 -> t3.g4 ->t1.g4 */
diff --git a/tool/src/org/antlr/v4/tool/Grammar.java b/tool/src/org/antlr/v4/tool/Grammar.java
index 549e1b056..45e945388 100644
--- a/tool/src/org/antlr/v4/tool/Grammar.java
+++ b/tool/src/org/antlr/v4/tool/Grammar.java
@@ -238,7 +238,7 @@ public class Grammar implements AttributeResolver {
 		org.antlr.runtime.ANTLRStringStream in = new org.antlr.runtime.ANTLRStringStream(grammarText);
 		in.name = fileName;
 
-		this.ast = tool.load(in);
+		this.ast = tool.load(fileName, in);
 		if ( ast==null ) return;
 
 		// ensure each node has pointer to surrounding grammar