diff --git a/guava/src/com/google/common/collect/ImmutableMap.java b/guava/src/com/google/common/collect/ImmutableMap.java
index e2e6cd5ae03f..b3a6b1943863 100644
--- a/guava/src/com/google/common/collect/ImmutableMap.java
+++ b/guava/src/com/google/common/collect/ImmutableMap.java
@@ -96,8 +96,11 @@ public abstract class ImmutableMap<K, V> implements Map<K, V>, Serializable {
    * and values are the result of applying the provided mapping functions to the input elements.
    *
    * <p>If the mapped keys contain duplicates (according to {@link Object#equals(Object)}), the
-   * values are merged using the specified merging function. Entries will appear in the encounter
-   * order of the first occurrence of the key.
+   * values are merged using the specified merging function. If the merging function returns {@code
+   * null}, then the collector removes the value that has been computed for the key thus far (though
+   * future occurrences of the key would reinsert it).
+   *
+   * <p>Entries will appear in the encounter order of the first occurrence of the key.
    *
    * @since 21.0
    */