diff --git a/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableBidiMap.java b/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableBidiMap.java
index 5faa5506d..e7855783a 100644
--- a/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableBidiMap.java
+++ b/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableBidiMap.java
@@ -52,6 +52,7 @@ public final class UnmodifiableBidiMap<K, V>
      * @param map  the map to decorate, must not be null
      * @return an unmodifiable BidiMap
      * @throws IllegalArgumentException if map is null
+     * @since 4.0
      */
     public static <K, V> BidiMap<K, V> unmodifiableBidiMap(final BidiMap<K, V> map) {
         if (map instanceof Unmodifiable) {
diff --git a/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableOrderedBidiMap.java b/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableOrderedBidiMap.java
index 9f8d7df55..64e92fd8f 100644
--- a/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableOrderedBidiMap.java
+++ b/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableOrderedBidiMap.java
@@ -52,6 +52,7 @@ public final class UnmodifiableOrderedBidiMap<K, V>
      * @param map  the map to decorate, must not be null
      * @return an unmodifiable OrderedBidiMap
      * @throws IllegalArgumentException if map is null
+     * @since 4.0
      */
     public static <K, V> OrderedBidiMap<K, V> unmodifiableOrderedBidiMap(final OrderedBidiMap<K, V> map) {
         if (map instanceof Unmodifiable) {
diff --git a/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableSortedBidiMap.java b/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableSortedBidiMap.java
index 4462f0fc5..9d0353c96 100644
--- a/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableSortedBidiMap.java
+++ b/src/main/java/org/apache/commons/collections4/bidimap/UnmodifiableSortedBidiMap.java
@@ -54,6 +54,7 @@ public final class UnmodifiableSortedBidiMap<K, V>
      * @param map  the map to decorate, must not be null
      * @return an unmodifiable SortedBidiMap
      * @throws IllegalArgumentException if map is null
+     * @since 4.0
      */
     public static <K, V> SortedBidiMap<K, V> unmodifiableSortedBidiMap(final SortedBidiMap<K, V> map) {
         if (map instanceof Unmodifiable) {