diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/ATN.java b/runtime/Java/src/org/antlr/v4/runtime/atn/ATN.java
index 763166d1a..420ef991d 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/ATN.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/ATN.java
@@ -46,7 +46,6 @@ public class ATN {
 
 	public static final int PARSER = 1;
 	public static final int LEXER = 2;
-	public static final int TREE_PARSER = 3;
 
 	@NotNull
 	public final List<ATNState> states = new ArrayList<ATNState>();
diff --git a/tool/src/org/antlr/v4/automata/ATNSerializer.java b/tool/src/org/antlr/v4/automata/ATNSerializer.java
index c989a4f8a..41c95300a 100644
--- a/tool/src/org/antlr/v4/automata/ATNSerializer.java
+++ b/tool/src/org/antlr/v4/automata/ATNSerializer.java
@@ -90,9 +90,20 @@ public class ATNSerializer {
 		IntegerList data = new IntegerList();
 		data.add(ATNSimulator.SERIALIZED_VERSION);
 		// convert grammar type to ATN const to avoid dependence on ANTLRParser
-		if ( g.getType()== ANTLRParser.LEXER ) data.add(ATN.LEXER);
-		else if ( g.getType()== ANTLRParser.PARSER ) data.add(ATN.PARSER);
-		else data.add(ATN.TREE_PARSER);
+		switch (g.getType()) {
+		case ANTLRParser.LEXER:
+			data.add(ATN.LEXER);
+			break;
+
+		case ANTLRParser.PARSER:
+		case ANTLRParser.COMBINED:
+			data.add(ATN.PARSER);
+			break;
+
+		default:
+			throw new UnsupportedOperationException("Invalid grammar type.");
+		}
+
 		data.add(g.getMaxTokenType());
 		int nedges = 0;