diff --git a/RELEASE-NOTES.txt b/RELEASE-NOTES.txt
index a2b107616..756c88f6d 100644
--- a/RELEASE-NOTES.txt
+++ b/RELEASE-NOTES.txt
@@ -47,6 +47,8 @@ Major changes since 3.2.1
 Changes since 4.0-alpha1
 ------------------------
 
+ o [COLLECTIONS-495] "UnmodifiableTrie#unmodifiableTrie(Trie)" will not decorate again an already unmodifiable Trie.
+                     Also the return type has been changed to "Trie" to be consistent with other Unmodifiable decorators.
  o [COLLECTIONS-494] Moved "Equator" interface to base package for consistency. Thanks to Emmanuel Bourg.
  o [COLLECTIONS-488] Added "CollectionsUtils#matchesAll(Iterable, Predicate)" to test if all elements
                      of a collection match a given predicate. Thanks to Josh Cain.
@@ -159,6 +161,8 @@ New features
 Changed classes / methods
 -------------------------
 
+ o [COLLECTIONS-495] "UnmodifiableTrie#unmodifiableTrie(Trie)" will not decorate again an already unmodifiable Trie.
+                     Also the return type has been changed to "Trie" to be consistent with other Unmodifiable decorators.
  o [COLLECTIONS-494] Moved "Equator" interface to base package for consistency. Thanks to Emmanuel Bourg.
  o [COLLECTIONS-485] Accept wildcard input where possible, e.g. in copy-constructors, Unmodifiable* decorators
                      and iterators. Thanks to Hollis Waite.
diff --git a/src/changes/changes.xml b/src/changes/changes.xml
index d2cff28eb..b7e7130c3 100644
--- a/src/changes/changes.xml
+++ b/src/changes/changes.xml
@@ -38,6 +38,11 @@ Commons Collections is Java 5.
 Users are encouraged to upgrade to this version as, in addition to new
 features, this release includes numerous bug fixes.
   ">
+    <action issue="COLLECTIONS-495" dev="tn" type="fix">
+     "UnmodifiableTrie#unmodifiableTrie(Trie)" will not decorate again an already
+     unmodifiable Trie. Also the return type has been changed to "Trie" to be consistent
+     with other Unmodifiable decorators.
+    </action>
     <action issue="COLLECTIONS-494" dev="tn" type="update" due-to="Emmanuel Bourg">
      Moved "Equator" interface to base package for consistency.
     </action>
diff --git a/src/main/java/org/apache/commons/collections4/trie/UnmodifiableTrie.java b/src/main/java/org/apache/commons/collections4/trie/UnmodifiableTrie.java
index 3d78550c7..feb47d639 100644
--- a/src/main/java/org/apache/commons/collections4/trie/UnmodifiableTrie.java
+++ b/src/main/java/org/apache/commons/collections4/trie/UnmodifiableTrie.java
@@ -51,7 +51,12 @@ public class UnmodifiableTrie<K, V> implements Trie<K, V>, Serializable, Unmodif
      * @return a new unmodifiable trie
      * @throws IllegalArgumentException if trie is null
      */
-    public static <K, V> UnmodifiableTrie<K, V> unmodifiableTrie(final Trie<K, ? extends V> trie) {
+    public static <K, V> Trie<K, V> unmodifiableTrie(final Trie<K, ? extends V> trie) {
+        if (trie instanceof Unmodifiable) {
+            @SuppressWarnings("unchecked") // safe to upcast
+            final Trie<K, V> tmpTrie = (Trie<K, V>) trie;
+            return tmpTrie;
+        }
         return new UnmodifiableTrie<K, V>(trie);
     }
 
diff --git a/src/site/xdoc/release_4_0.xml b/src/site/xdoc/release_4_0.xml
index 5f4bc4fa9..60e8b82bd 100644
--- a/src/site/xdoc/release_4_0.xml
+++ b/src/site/xdoc/release_4_0.xml
@@ -155,6 +155,8 @@ have changed.
 
 <center><h3>Changed classes / methods</h3></center>
 <ul>
+<li>"UnmodifiableTrie#unmodifiableTrie(Trie)" will not decorate again an already unmodifiable Trie.
+     Also the return type has been changed to "Trie" to be consistent with other Unmodifiable decorators.</li>
 <li>Moved "Equator" interface to base package for consistency.</li>
 <li>Accept wildcard input where possible, e.g. in copy-constructors, Unmodifiable* decorators and iterators.</li>
 <li>Narrow return type of "BidiMap#values()" to Set as the values are required to be unique.</li>
diff --git a/src/test/java/org/apache/commons/collections4/TrieUtilsTest.java b/src/test/java/org/apache/commons/collections4/TrieUtilsTest.java
index c473fd0f9..36badbef5 100644
--- a/src/test/java/org/apache/commons/collections4/TrieUtilsTest.java
+++ b/src/test/java/org/apache/commons/collections4/TrieUtilsTest.java
@@ -49,6 +49,8 @@ public class TrieUtilsTest extends BulkTest {
         } catch (final IllegalArgumentException ex) {
             // expected
         }
+        
+        assertSame("UnmodifiableTrie shall not be decorated", trie, TrieUtils.unmodifiableTrie(trie));
     }
 
 }
diff --git a/src/test/java/org/apache/commons/collections4/trie/UnmodifiableTrieTest.java b/src/test/java/org/apache/commons/collections4/trie/UnmodifiableTrieTest.java
index 28dd8630a..e4eb48be0 100644
--- a/src/test/java/org/apache/commons/collections4/trie/UnmodifiableTrieTest.java
+++ b/src/test/java/org/apache/commons/collections4/trie/UnmodifiableTrieTest.java
@@ -16,14 +16,12 @@
  */
 package org.apache.commons.collections4.trie;
 
-import java.util.SortedMap;
-
 import junit.framework.Test;
 
 import org.apache.commons.collections4.BulkTest;
+import org.apache.commons.collections4.Trie;
 import org.apache.commons.collections4.Unmodifiable;
 import org.apache.commons.collections4.map.AbstractSortedMapTest;
-import org.apache.commons.collections4.map.UnmodifiableSortedMap;
 
 /**
  * Extension of {@link AbstractSortedMapTest} for exercising the
@@ -45,8 +43,8 @@ public class UnmodifiableTrieTest<V> extends AbstractSortedMapTest<String, V> {
     //-------------------------------------------------------------------
 
     @Override
-    public SortedMap<String, V> makeObject() {
-        return UnmodifiableSortedMap.unmodifiableSortedMap(new PatriciaTrie<V>());
+    public Trie<String, V> makeObject() {
+        return UnmodifiableTrie.unmodifiableTrie(new PatriciaTrie<V>());
     }
 
     @Override
@@ -65,28 +63,31 @@ public class UnmodifiableTrieTest<V> extends AbstractSortedMapTest<String, V> {
     }
 
     @Override
-    public SortedMap<String, V> makeFullMap() {
-        final SortedMap<String, V> m = new PatriciaTrie<V>();
+    public Trie<String, V> makeFullMap() {
+        final Trie<String, V> m = new PatriciaTrie<V>();
         addSampleMappings(m);
-        return UnmodifiableSortedMap.unmodifiableSortedMap(m);
+        return UnmodifiableTrie.unmodifiableTrie(m);
     }
 
     //-----------------------------------------------------------------------
+
     public void testUnmodifiable() {
         assertTrue(makeObject() instanceof Unmodifiable);
         assertTrue(makeFullMap() instanceof Unmodifiable);
     }
 
     public void testDecorateFactory() {
-        final SortedMap<String, V> map = makeFullMap();
-        assertSame(map, UnmodifiableSortedMap.unmodifiableSortedMap(map));
+        final Trie<String, V> trie = makeFullMap();
+        assertSame(trie, UnmodifiableTrie.unmodifiableTrie(trie));
 
         try {
-            UnmodifiableSortedMap.unmodifiableSortedMap(null);
+            UnmodifiableTrie.unmodifiableTrie(null);
             fail();
         } catch (final IllegalArgumentException ex) {}
     }
 
+    //-----------------------------------------------------------------------
+
     @Override
     public String getCompatibilityVersion() {
         return "4";