diff --git a/src/java.base/share/classes/java/util/HashSet.java b/src/java.base/share/classes/java/util/HashSet.java
index 02dc0b4ee9d..43401224059 100644
--- a/src/java.base/share/classes/java/util/HashSet.java
+++ b/src/java.base/share/classes/java/util/HashSet.java
@@ -382,12 +382,12 @@ public Spliterator<E> spliterator() {
     }
 
     @Override
-    public Object[] toArray() {
+    public @Nullable Object[] toArray() {
         return map.keysToArray(new Object[map.size()]);
     }
 
     @Override
-    public <T> T[] toArray(T[] a) {
+    public <T extends @Nullable Object> T[] toArray(T[] a) {
         return map.keysToArray(map.prepareArray(a));
     }
 
diff --git a/src/java.base/share/classes/java/util/IdentityHashMap.java b/src/java.base/share/classes/java/util/IdentityHashMap.java
index f17ce1e0298..80a90dc8976 100644
--- a/src/java.base/share/classes/java/util/IdentityHashMap.java
+++ b/src/java.base/share/classes/java/util/IdentityHashMap.java
@@ -1444,7 +1444,7 @@ public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
      * {@code false}.
      */
     @Override
-    public boolean remove(Object key, Object value) {
+    public boolean remove(@Nullable Object key, @Nullable Object value) {
         return removeMapping(key, value);
     }
 
diff --git a/src/java.base/share/classes/java/util/TreeMap.java b/src/java.base/share/classes/java/util/TreeMap.java
index f28c046aafe..9f65dec28a3 100644
--- a/src/java.base/share/classes/java/util/TreeMap.java
+++ b/src/java.base/share/classes/java/util/TreeMap.java
@@ -25,6 +25,7 @@
 
 package java.util;
 
+import org.jspecify.annotations.NonNull;
 import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
@@ -581,7 +582,7 @@ final Entry<K,V> getLowerEntry(K key) {
     }
 
     @Override
-    public V putIfAbsent(K key, V value) {
+    public @Nullable V putIfAbsent(K key, V value) {
         return put(key, value, false);
     }
 
@@ -666,7 +667,7 @@ else if (cmp > 0)
      * remapping function modified this map
      */
     @Override
-    public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+    public @Nullable V computeIfPresent(K key, BiFunction<? super K, ? super @NonNull V, ? extends @Nullable V> remappingFunction) {
         Objects.requireNonNull(remappingFunction);
         Entry<K,V> oldEntry = getEntry(key);
         if (oldEntry != null && oldEntry.value != null) {
@@ -687,7 +688,7 @@ public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> r
      * remapping function modified this map
      */
     @Override
-    public V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
+    public @Nullable V compute(K key, BiFunction<? super K, ? super @Nullable V, ? extends @Nullable V> remappingFunction) {
         Objects.requireNonNull(remappingFunction);
         V newValue;
         Entry<K,V> t = root;
@@ -749,7 +750,7 @@ else if (cmp > 0)
      * remapping function modified this map
      */
     @Override
-    public V merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
+    public @Nullable V merge(K key, @NonNull V value, BiFunction<? super @NonNull V, ? super @NonNull V, ? extends @Nullable V> remappingFunction) {
         Objects.requireNonNull(remappingFunction);
         Objects.requireNonNull(value);
         Entry<K,V> t = root;