diff --git a/src/main/org/apache/tools/ant/listener/ProfileLogger.java b/src/main/org/apache/tools/ant/listener/ProfileLogger.java
index 86cc8604d..bbf5bb4fa 100644
--- a/src/main/org/apache/tools/ant/listener/ProfileLogger.java
+++ b/src/main/org/apache/tools/ant/listener/ProfileLogger.java
@@ -18,8 +18,8 @@
 package org.apache.tools.ant.listener;
 
 import java.util.Date;
-import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.apache.tools.ant.BuildEvent;
 import org.apache.tools.ant.DefaultLogger;
@@ -32,7 +32,7 @@ import org.apache.tools.ant.util.StringUtils;
  */
 public class ProfileLogger extends DefaultLogger {
 
-    private Map<Object, Date> profileData = new HashMap<Object, Date>();
+    private Map<Object, Date> profileData = new ConcurrentHashMap<Object, Date>();
 
     /**
      * Logs a message to say that the target has started.
diff --git a/src/main/org/apache/tools/zip/ExtraFieldUtils.java b/src/main/org/apache/tools/zip/ExtraFieldUtils.java
index 396ab4d1b..a6c0118ff 100644
--- a/src/main/org/apache/tools/zip/ExtraFieldUtils.java
+++ b/src/main/org/apache/tools/zip/ExtraFieldUtils.java
@@ -19,9 +19,9 @@
 package org.apache.tools.zip;
 
 import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.zip.ZipException;
 
 /**
@@ -41,7 +41,7 @@ public class ExtraFieldUtils {
     private static final Map<ZipShort, Class<?>> implementations;
 
     static {
-        implementations = new HashMap<ZipShort, Class<?>>();
+        implementations = new ConcurrentHashMap<ZipShort, Class<?>>();
         register(AsiExtraField.class);
         register(JarMarker.class);
         register(UnicodePathExtraField.class);
diff --git a/src/main/org/apache/tools/zip/ZipEncodingHelper.java b/src/main/org/apache/tools/zip/ZipEncodingHelper.java
index 9c17c9ec8..f4ca79d19 100644
--- a/src/main/org/apache/tools/zip/ZipEncodingHelper.java
+++ b/src/main/org/apache/tools/zip/ZipEncodingHelper.java
@@ -21,6 +21,7 @@ package org.apache.tools.zip;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
 import java.nio.charset.UnsupportedCharsetException;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -65,7 +66,8 @@ public abstract class ZipEncodingHelper {
     private static final Map<String, SimpleEncodingHolder> simpleEncodings;
 
     static {
-        simpleEncodings = new HashMap<String, SimpleEncodingHolder>();
+        Map<String, SimpleEncodingHolder> se =
+            new HashMap<String, SimpleEncodingHolder>();
 
         char[] cp437_high_chars =
             new char[] { 0x00c7, 0x00fc, 0x00e9, 0x00e2, 0x00e4, 0x00e0,
@@ -93,11 +95,11 @@ public abstract class ZipEncodingHelper {
 
         SimpleEncodingHolder cp437 = new SimpleEncodingHolder(cp437_high_chars);
 
-        simpleEncodings.put("CP437",cp437);
-        simpleEncodings.put("Cp437",cp437);
-        simpleEncodings.put("cp437",cp437);
-        simpleEncodings.put("IBM437",cp437);
-        simpleEncodings.put("ibm437",cp437);
+        se.put("CP437", cp437);
+        se.put("Cp437", cp437);
+        se.put("cp437", cp437);
+        se.put("IBM437", cp437);
+        se.put("ibm437", cp437);
 
         char[] cp850_high_chars =
             new char[] { 0x00c7, 0x00fc, 0x00e9, 0x00e2, 0x00e4, 0x00e0,
@@ -125,11 +127,12 @@ public abstract class ZipEncodingHelper {
 
         SimpleEncodingHolder cp850 = new SimpleEncodingHolder(cp850_high_chars);
 
-        simpleEncodings.put("CP850",cp850);
-        simpleEncodings.put("Cp850",cp850);
-        simpleEncodings.put("cp850",cp850);
-        simpleEncodings.put("IBM850",cp850);
-        simpleEncodings.put("ibm850",cp850);
+        se.put("CP850", cp850);
+        se.put("Cp850", cp850);
+        se.put("cp850", cp850);
+        se.put("IBM850", cp850);
+        se.put("ibm850", cp850);
+        simpleEncodings = Collections.unmodifiableMap(se);
     }
 
     /**