diff --git a/CHANGES.txt b/CHANGES.txt
index 13454f223..2b0ee2cdc 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -7,6 +7,7 @@ December 11, 2012
 * Listen for issues reported by StringTemplate, report them as warnings
 * Fix template issues
 * GrammarASTWithOptions.getOptions never returns null
+* Use EnumSet instead of HashSet
 
 December 2, 2012
 
diff --git a/tool/src/org/antlr/v4/tool/ErrorManager.java b/tool/src/org/antlr/v4/tool/ErrorManager.java
index 17c2ff6d4..441cc729d 100644
--- a/tool/src/org/antlr/v4/tool/ErrorManager.java
+++ b/tool/src/org/antlr/v4/tool/ErrorManager.java
@@ -40,7 +40,7 @@ import org.stringtemplate.v4.misc.STMessage;
 
 import java.net.URL;
 import java.util.Collection;
-import java.util.HashSet;
+import java.util.EnumSet;
 import java.util.Locale;
 import java.util.Set;
 
@@ -52,7 +52,7 @@ public class ErrorManager {
 	public int warnings;
 
 	/** All errors that have been generated */
-	public Set<ErrorType> errorTypes = new HashSet<ErrorType>();
+	public Set<ErrorType> errorTypes = EnumSet.noneOf(ErrorType.class);
 
     /** The group of templates that represent the current message format. */
     STGroup format;