diff --git a/classlib/src/main/java/org/teavm/classlib/java/util/TIdentityHashMap.java b/classlib/src/main/java/org/teavm/classlib/java/util/TIdentityHashMap.java
new file mode 100644
index 000000000..6481e672e
--- /dev/null
+++ b/classlib/src/main/java/org/teavm/classlib/java/util/TIdentityHashMap.java
@@ -0,0 +1,621 @@
+/*
+ *  Copyright 2014 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one or more
+ *  contributor license agreements.  See the NOTICE file distributed with
+ *  this work for additional information regarding copyright ownership.
+ *  The ASF licenses this file to You under the Apache License, Version 2.0
+ *  (the "License"); you may not use this file except in compliance with
+ *  the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package org.teavm.classlib.java.util;
+
+import java.util.Arrays;
+import java.util.ConcurrentModificationException;
+import org.teavm.classlib.java.io.TSerializable;
+import org.teavm.classlib.java.lang.TCloneNotSupportedException;
+import org.teavm.classlib.java.lang.TCloneable;
+import org.teavm.classlib.java.lang.TIllegalArgumentException;
+import org.teavm.classlib.java.lang.TIllegalStateException;
+import org.teavm.classlib.java.lang.TObject;
+import org.teavm.interop.Rename;
+
+public class TIdentityHashMap<K, V> extends TAbstractMap<K, V> implements TCloneable, TSerializable {
+    transient int elementCount;
+    transient HashEntry<K, V>[] elementData;
+    transient int modCount;
+    private static final int DEFAULT_SIZE = 16;
+    final float loadFactor;
+    int threshold;
+
+    static class HashEntry<K, V> extends TMapEntry<K, V> {
+        final int origKeyHash;
+
+        HashEntry<K, V> next;
+
+        HashEntry(K theKey, int hash) {
+            super(theKey, null);
+            this.origKeyHash = hash;
+        }
+
+        HashEntry(K theKey, V theValue) {
+            super(theKey, theValue);
+            origKeyHash = theKey == null ? 0 : computeHashCode(theKey);
+        }
+
+        @Override
+        @SuppressWarnings("unchecked")
+        public Object clone() {
+            HashEntry<K, V> entry = (HashEntry<K, V>) super.clone();
+            if (next != null) {
+                entry.next = (HashEntry<K, V>) next.clone();
+            }
+            return entry;
+        }
+    }
+
+    private static class AbstractMapIterator<K, V>  {
+        private int position;
+        int expectedModCount;
+        HashEntry<K, V> futureEntry;
+        HashEntry<K, V> currentEntry;
+        HashEntry<K, V> prevEntry;
+
+        final TIdentityHashMap<K, V> associatedMap;
+
+        AbstractMapIterator(TIdentityHashMap<K, V> hm) {
+            associatedMap = hm;
+            expectedModCount = hm.modCount;
+            futureEntry = null;
+        }
+
+        public boolean hasNext() {
+            if (futureEntry != null) {
+                return true;
+            }
+            while (position < associatedMap.elementData.length) {
+                if (associatedMap.elementData[position] == null) {
+                    position++;
+                } else {
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        final void checkConcurrentMod() throws ConcurrentModificationException {
+            if (expectedModCount != associatedMap.modCount) {
+                throw new TConcurrentModificationException();
+            }
+        }
+
+        final void makeNext() {
+            checkConcurrentMod();
+            if (!hasNext()) {
+                throw new TNoSuchElementException();
+            }
+            if (futureEntry == null) {
+                currentEntry = associatedMap.elementData[position++];
+                futureEntry = currentEntry.next;
+                prevEntry = null;
+            } else {
+                if (currentEntry != null) {
+                    prevEntry = currentEntry;
+                }
+                currentEntry = futureEntry;
+                futureEntry = futureEntry.next;
+            }
+        }
+
+        public final void remove() {
+            checkConcurrentMod();
+            if (currentEntry == null) {
+                throw new TIllegalStateException();
+            }
+            if (prevEntry == null) {
+                int index = currentEntry.origKeyHash & (associatedMap.elementData.length - 1);
+                associatedMap.elementData[index] = associatedMap.elementData[index].next;
+            } else {
+                prevEntry.next = currentEntry.next;
+            }
+            currentEntry = null;
+            expectedModCount++;
+            associatedMap.modCount++;
+            associatedMap.elementCount--;
+
+        }
+    }
+
+
+    private static class EntryIterator<K, V> extends AbstractMapIterator<K, V>
+            implements TIterator<Entry<K, V>> {
+        EntryIterator(TIdentityHashMap<K, V> map) {
+            super(map);
+        }
+
+        @Override
+        public Entry<K, V> next() {
+            makeNext();
+            return currentEntry;
+        }
+    }
+
+    private static class KeyIterator<K, V> extends AbstractMapIterator<K, V> implements TIterator<K> {
+        KeyIterator(TIdentityHashMap<K, V> map) {
+            super(map);
+        }
+
+        @Override
+        public K next() {
+            makeNext();
+            return currentEntry.key;
+        }
+    }
+
+    private static class ValueIterator<K, V> extends AbstractMapIterator<K, V> implements TIterator<V> {
+        ValueIterator(TIdentityHashMap<K, V> map) {
+            super(map);
+        }
+
+        @Override
+        public V next() {
+            makeNext();
+            return currentEntry.value;
+        }
+    }
+
+    static class HashMapEntrySet<K, V> extends TAbstractSet<Entry<K, V>> {
+        private final TIdentityHashMap<K, V> associatedMap;
+
+        public HashMapEntrySet(TIdentityHashMap<K, V> hm) {
+            associatedMap = hm;
+        }
+
+        TIdentityHashMap<K, V> hashMap() {
+            return associatedMap;
+        }
+
+        @Override
+        public int size() {
+            return associatedMap.elementCount;
+        }
+
+        @Override
+        public void clear() {
+            associatedMap.clear();
+        }
+
+        @Override
+        public boolean remove(Object object) {
+            if (object instanceof TMap.Entry) {
+                Entry<?, ?> oEntry = (Entry<?, ?>) object;
+                Entry<K, V> entry = associatedMap.getEntry(oEntry.getKey());
+                if (valuesEq(entry, oEntry)) {
+                    associatedMap.removeEntry(entry);
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        @Override
+        public boolean contains(Object object) {
+            if (object instanceof TMap.Entry) {
+                Entry<?, ?> oEntry = (Entry<?, ?>) object;
+                Entry<K, V> entry = associatedMap.getEntry(oEntry.getKey());
+                return valuesEq(entry, oEntry);
+            }
+            return false;
+        }
+
+        private static boolean valuesEq(Entry<?, ?> entry, Entry<?, ?> oEntry) {
+            return entry != null
+                    && (entry.getValue() == null
+                    ? oEntry.getValue() == null
+                    : areSameValues(entry.getValue(), oEntry.getValue()));
+        }
+
+        @Override
+        public TIterator<Entry<K, V>> iterator() {
+            return new EntryIterator<>(associatedMap);
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    HashEntry<K, V>[] newElementArray(int s) {
+        return new HashEntry[s];
+    }
+
+    public TIdentityHashMap() {
+        this(DEFAULT_SIZE);
+    }
+
+    public TIdentityHashMap(int capacity) {
+        this(capacity, 0.75f);  // default load factor of 0.75
+    }
+
+    private static int calculateCapacity(int x) {
+        if (x >= 1 << 30) {
+            return 1 << 30;
+        }
+        if (x == 0) {
+            return 16;
+        }
+        x = x - 1;
+        x |= x >> 1;
+        x |= x >> 2;
+        x |= x >> 4;
+        x |= x >> 8;
+        x |= x >> 16;
+        return x + 1;
+    }
+
+    /**
+     * Constructs a new {@code HashMap} instance with the specified capacity and
+     * load factor.
+     *
+     * @param capacity
+     *            the initial capacity of this hash map.
+     * @param loadFactor
+     *            the initial load factor.
+     * @throws IllegalArgumentException
+     *                when the capacity is less than zero or the load factor is
+     *                less or equal to zero.
+     */
+    public TIdentityHashMap(int capacity, float loadFactor) {
+        if (capacity >= 0 && loadFactor > 0) {
+            capacity = calculateCapacity(capacity);
+            elementCount = 0;
+            elementData = newElementArray(capacity);
+            this.loadFactor = loadFactor;
+            computeThreshold();
+        } else {
+            throw new TIllegalArgumentException();
+        }
+    }
+
+    public TIdentityHashMap(TMap<? extends K, ? extends V> map) {
+        this(calculateCapacity(map.size()));
+        putAllImpl(map);
+    }
+
+    @Override
+    public void clear() {
+        if (elementCount > 0) {
+            elementCount = 0;
+            Arrays.fill(elementData, null);
+            modCount++;
+        }
+    }
+
+    @Rename("clone")
+    @SuppressWarnings("unchecked")
+    public TObject clone0() {
+        try {
+            TIdentityHashMap<K, V> map = (TIdentityHashMap<K, V>) super.clone();
+            map.elementCount = 0;
+            map.elementData = newElementArray(elementData.length);
+            map.putAll(this);
+
+            return map;
+        } catch (TCloneNotSupportedException e) {
+            return null;
+        }
+    }
+
+    private void computeThreshold() {
+        threshold = (int) (elementData.length * loadFactor);
+    }
+
+    @Override
+    public boolean containsKey(Object key) {
+        HashEntry<K, V> m = getEntry(key);
+        return m != null;
+    }
+
+    @Override
+    public boolean containsValue(Object value) {
+        if (value != null) {
+            for (int i = 0; i < elementData.length; i++) {
+                HashEntry<K, V> entry = elementData[i];
+                while (entry != null) {
+                    if (areSameValues(value, entry.value)) {
+                        return true;
+                    }
+                    entry = entry.next;
+                }
+            }
+        } else {
+            for (int i = 0; i < elementData.length; i++) {
+                HashEntry<K, V> entry = elementData[i];
+                while (entry != null) {
+                    if (entry.value == null) {
+                        return true;
+                    }
+                    entry = entry.next;
+                }
+            }
+        }
+        return false;
+    }
+
+    @Override
+    public TSet<Entry<K, V>> entrySet() {
+        return new HashMapEntrySet<>(this);
+    }
+
+    @Override
+    public V get(Object key) {
+        HashEntry<K, V> m = getEntry(key);
+        if (m != null) {
+            return m.value;
+        }
+        return null;
+    }
+
+    final HashEntry<K, V> getEntry(Object key) {
+        HashEntry<K, V> m;
+        if (key == null) {
+            m = findNullKeyEntry();
+        } else {
+            int hash = computeHashCode(key);
+            int index = hash & (elementData.length - 1);
+            m = findNonNullKeyEntry(key, index, hash);
+        }
+        return m;
+    }
+
+    final HashEntry<K, V> findNonNullKeyEntry(Object key, int index, int keyHash) {
+        HashEntry<K, V> m = elementData[index];
+        while (m != null
+                && (m.origKeyHash != keyHash || !areSameKeys(key, m.key))) {
+            m = m.next;
+        }
+        return m;
+    }
+
+    final HashEntry<K, V> findNullKeyEntry() {
+        HashEntry<K, V> m = elementData[0];
+        while (m != null && m.key != null) {
+            m = m.next;
+        }
+        return m;
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return elementCount == 0;
+    }
+
+    @Override
+    public TSet<K> keySet() {
+        if (cachedKeySet == null) {
+            cachedKeySet = new TAbstractSet<K>() {
+                @Override public boolean contains(Object object) {
+                    return containsKey(object);
+                }
+                @Override public int size() {
+                    return TIdentityHashMap.this.size();
+                }
+                @Override public void clear() {
+                    TIdentityHashMap.this.clear();
+                }
+                @Override public boolean remove(Object key) {
+                    HashEntry<K, V> entry = TIdentityHashMap.this.removeEntry(key);
+                    return entry != null;
+                }
+                @Override public TIterator<K> iterator() {
+                    return new KeyIterator<>(TIdentityHashMap.this);
+                }
+            };
+        }
+        return cachedKeySet;
+    }
+
+    @Override
+    public V put(K key, V value) {
+        return putImpl(key, value);
+    }
+
+    V putImpl(K key, V value) {
+        HashEntry<K, V> entry;
+        if (key == null) {
+            entry = findNullKeyEntry();
+            if (entry == null) {
+                modCount++;
+                entry = createHashedEntry(null, 0, 0);
+                if (++elementCount > threshold) {
+                    rehash();
+                }
+            }
+        } else {
+            int hash = computeHashCode(key);
+            int index = hash & (elementData.length - 1);
+            entry = findNonNullKeyEntry(key, index, hash);
+            if (entry == null) {
+                modCount++;
+                entry = createHashedEntry(key, index, hash);
+                if (++elementCount > threshold) {
+                    rehash();
+                }
+            }
+        }
+
+        V result = entry.value;
+        entry.value = value;
+        return result;
+    }
+
+    HashEntry<K, V> createEntry(K key, int index, V value) {
+        HashEntry<K, V> entry = new HashEntry<>(key, value);
+        entry.next = elementData[index];
+        elementData[index] = entry;
+        return entry;
+    }
+
+    HashEntry<K, V> createHashedEntry(K key, int index, int hash) {
+        HashEntry<K, V> entry = new HashEntry<>(key, hash);
+        entry.next = elementData[index];
+        elementData[index] = entry;
+        return entry;
+    }
+
+    @Override
+    public void putAll(TMap<? extends K, ? extends V> map) {
+        if (!map.isEmpty()) {
+            putAllImpl(map);
+        }
+    }
+
+    private void putAllImpl(TMap<? extends K, ? extends V> map) {
+        int capacity = elementCount + map.size();
+        if (capacity > threshold) {
+            rehash(capacity);
+        }
+        for (TIterator<? extends Entry<? extends K, ? extends V>> iter = map.entrySet().iterator();
+                iter.hasNext();) {
+            Entry<? extends K, ? extends V> entry = iter.next();
+            putImpl(entry.getKey(), entry.getValue());
+        }
+    }
+
+    void rehash(int capacity) {
+        int length = calculateCapacity(capacity == 0 ? 1 : capacity << 1);
+
+        HashEntry<K, V>[] newData = newElementArray(length);
+        for (int i = 0; i < elementData.length; i++) {
+            HashEntry<K, V> entry = elementData[i];
+            elementData[i] = null;
+            while (entry != null) {
+                int index = entry.origKeyHash & (length - 1);
+                HashEntry<K, V> next = entry.next;
+                entry.next = newData[index];
+                newData[index] = entry;
+                entry = next;
+            }
+        }
+        elementData = newData;
+        computeThreshold();
+    }
+
+    void rehash() {
+        rehash(elementData.length);
+    }
+
+    @Override
+    public V remove(Object key) {
+        HashEntry<K, V> entry = removeEntry(key);
+        if (entry != null) {
+            return entry.value;
+        }
+        return null;
+    }
+
+    final void removeEntry(HashEntry<K, V> entry) {
+        int index = entry.origKeyHash & (elementData.length - 1);
+        HashEntry<K, V> m = elementData[index];
+        if (m == entry) {
+            elementData[index] = entry.next;
+        } else {
+            while (m.next != entry) {
+                m = m.next;
+            }
+            m.next = entry.next;
+
+        }
+        modCount++;
+        elementCount--;
+    }
+
+    final HashEntry<K, V> removeEntry(Object key) {
+        int index = 0;
+        HashEntry<K, V> entry;
+        HashEntry<K, V> last = null;
+        if (key != null) {
+            int hash = computeHashCode(key);
+            index = hash & (elementData.length - 1);
+            entry = elementData[index];
+            while (entry != null && !(entry.origKeyHash == hash && areSameKeys(key, entry.key))) {
+                last = entry;
+                entry = entry.next;
+            }
+        } else {
+            entry = elementData[0];
+            while (entry != null && entry.key != null) {
+                last = entry;
+                entry = entry.next;
+            }
+        }
+        if (entry == null) {
+            return null;
+        }
+        if (last == null) {
+            elementData[index] = entry.next;
+        } else {
+            last.next = entry.next;
+        }
+        modCount++;
+        elementCount--;
+        return entry;
+    }
+
+    @Override
+    public int size() {
+        return elementCount;
+    }
+
+    @Override
+    public TCollection<V> values() {
+        if (cachedValues == null) {
+            cachedValues = new TAbstractCollection<V>() {
+                @Override public boolean contains(Object object) {
+                    return containsValue(object);
+                }
+                @Override public int size() {
+                    return TIdentityHashMap.this.size();
+                }
+                @Override public void clear() {
+                    TIdentityHashMap.this.clear();
+                }
+                @Override public TIterator<V> iterator() {
+                    return new ValueIterator<>(TIdentityHashMap.this);
+                }
+            };
+        }
+        return cachedValues;
+    }
+
+    static int computeHashCode(Object key) {
+        return System.identityHashCode(key);
+    }
+
+    static boolean areSameKeys(Object key1, Object key2) {
+        return key1 == key2;
+    }
+
+    static boolean areSameValues(Object value1, Object value2) {
+        return value1 == value2;
+    }
+}
diff --git a/core/src/main/resources/org/teavm/backend/javascript/runtime.js b/core/src/main/resources/org/teavm/backend/javascript/runtime.js
index 196367c36..cbb559afc 100644
--- a/core/src/main/resources/org/teavm/backend/javascript/runtime.js
+++ b/core/src/main/resources/org/teavm/backend/javascript/runtime.js
@@ -15,15 +15,14 @@
  */
 "use strict";
 var $rt_global = this;
-var $rt_lastObjectId = 1;
+var $rt_seed = 2463534242;
 function $rt_nextId() {
-    var current = $rt_lastObjectId;
-    var next = (current + 1) | 0;
-    if (next === 0) {
-        next = (next + 1) | 0;
-    }
-    $rt_lastObjectId = next;
-    return current;
+    var x = $rt_seed;
+    x ^= x << 13;
+    x ^= x >> 17;
+    x ^= x << 5;
+    $rt_seed = x;
+    return x;
 }
 function $rt_compare(a, b) {
     return a > b ? 1 : a < b ? -1 : 0;
diff --git a/tests/src/test/java/org/teavm/classlib/java/util/IdentityHashMapTest.java b/tests/src/test/java/org/teavm/classlib/java/util/IdentityHashMapTest.java
new file mode 100644
index 000000000..d598f47ee
--- /dev/null
+++ b/tests/src/test/java/org/teavm/classlib/java/util/IdentityHashMapTest.java
@@ -0,0 +1,113 @@
+/*
+ *  Copyright 2014 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+/*
+ *  Licensed to the Apache Software Foundation (ASF) under one or more
+ *  contributor license agreements.  See the NOTICE file distributed with
+ *  this work for additional information regarding copyright ownership.
+ *  The ASF licenses this file to You under the Apache License, Version 2.0
+ *  (the "License"); you may not use this file except in compliance with
+ *  the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package org.teavm.classlib.java.util;
+
+import static org.junit.Assert.assertEquals;
+import java.util.IdentityHashMap;
+import java.util.Map;
+import java.util.Objects;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.teavm.junit.TeaVMTestRunner;
+
+@RunWith(TeaVMTestRunner.class)
+public class IdentityHashMapTest {
+
+    @Test
+    public void sameObjectOnce() {
+        Map<Object, Object> m = new IdentityHashMap<>();
+        Object key = new Object();
+        m.put(key, "val1");
+        m.put(key, "val2");
+        assertEquals(1, m.keySet().size());
+    }
+
+    @Test
+    public void twoObjectsTwice() {
+        Map<Object, Object> m = new IdentityHashMap<>();
+        Object key1 = new Object();
+        Object key2 = new Object();
+        m.put(key1, "val1");
+        m.put(key2, "val2");
+        assertEquals(2, m.size());
+        assertEquals("val1", m.get(key1));
+        assertEquals("val2", m.get(key2));
+    }
+
+    @Test
+    public void twoObjectsWithSameHashCode() {
+        Map<A, Object> m = new IdentityHashMap<>();
+        A key1 = new A("ciao");
+        A key2 = new A("ciao");
+        m.put(key1, "val1");
+        m.put(key2, "val2");
+        assertEquals(2, m.size());
+        assertEquals("val1", m.get(key1));
+        assertEquals("val2", m.get(key2));
+    }
+
+    @Test
+    public void nullKeyAllowed() {
+        Map<String, String> m = new IdentityHashMap<>();
+        m.put(null, "val1");
+        m.put(null, "val2");
+        assertEquals(1, m.size());
+        assertEquals("val2", m.get(null));
+    }
+
+    static class A {
+        public A(String b) {
+            this.b = b;
+        }
+
+        private String b;
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) {
+                return true;
+            }
+            if (o == null || getClass() != o.getClass()) {
+                return false;
+            }
+            A a = (A) o;
+            return Objects.equals(b, a.b);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(b);
+        }
+    }
+}