diff --git a/classlib/src/main/java/org/teavm/classlib/java/lang/TClass.java b/classlib/src/main/java/org/teavm/classlib/java/lang/TClass.java
index b453ee394..f441fc46f 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/lang/TClass.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/lang/TClass.java
@@ -512,7 +512,7 @@ public class TClass<T> extends TObject implements TAnnotatedElement {
 
     @SuppressWarnings("unchecked")
     public T[] getEnumConstants() {
-        return isEnum() ? (T[]) Platform.getEnumConstants(platformClass) : null;
+        return isEnum() ? (T[]) Platform.getEnumConstants(platformClass).clone() : null;
     }
 
     @SuppressWarnings("unchecked")
diff --git a/classlib/src/main/java/org/teavm/classlib/java/util/TEnumSet.java b/classlib/src/main/java/org/teavm/classlib/java/util/TEnumSet.java
new file mode 100644
index 000000000..ee407157a
--- /dev/null
+++ b/classlib/src/main/java/org/teavm/classlib/java/util/TEnumSet.java
@@ -0,0 +1,117 @@
+package org.teavm.classlib.java.util;
+
+import java.io.Serializable;
+import java.util.AbstractSet;
+import java.util.Collection;
+import java.util.Iterator;
+
+public abstract class TEnumSet<E extends Enum<E>> extends AbstractSet<E> implements Cloneable, Serializable {
+    public static <E extends Enum<E>> TEnumSet<E> noneOf(Class<E> elementType) {
+        return new TGenericEnumSet<>(elementType);
+    }
+
+    public static <E extends Enum<E>> TEnumSet<E> allOf(Class<E> elementType) {
+        int count = TGenericEnumSet.getConstants(elementType).length;
+        int[] bits = new int[((count - 1) / 32) + 1];
+        for (int i = 0; i < bits.length; ++i) {
+            bits[i] = ~0;
+        }
+        zeroHighBits(bits, count);
+        return new TGenericEnumSet<>(elementType, bits);
+    }
+
+    public static <E extends Enum<E>> TEnumSet<E> copyOf(TEnumSet<E> s) {
+        TGenericEnumSet<E> other = (TGenericEnumSet<E>) s;
+        return new TGenericEnumSet<>(other.cls, other.bits.clone());
+    }
+
+    public static <E extends Enum<E>> TEnumSet<E> copyOf(Collection<E> c) {
+        if (c instanceof TEnumSet<?>) {
+            return copyOf((TEnumSet<E>) c);
+        } else {
+            Iterator<E> iter = c.iterator();
+            if (!iter.hasNext()) {
+                throw new IllegalArgumentException();
+            }
+            E first = iter.next();
+            @SuppressWarnings("unchecked")
+            TEnumSet<E> result = noneOf(first.getDeclaringClass());
+            result.add(first);
+            while (iter.hasNext()) {
+                result.add(iter.next());
+            }
+            return result;
+        }
+    }
+
+    public static <E extends Enum<E>> TEnumSet<E> complementOf(TEnumSet<E> s) {
+        TGenericEnumSet<E> other = (TGenericEnumSet<E>) s;
+        int count = TGenericEnumSet.getConstants(other.cls).length;
+        int[] bits = new int[other.bits.length];
+        for (int i = 0; i < bits.length - 1; ++i) {
+            bits[i] = ~other.bits[i];
+        }
+        zeroHighBits(bits, count);
+        return new TGenericEnumSet<>(other.cls, bits);
+    }
+
+    public static <E extends Enum<E>> TEnumSet<E> of(E e) {
+        TEnumSet<E> result = TEnumSet.noneOf(e.getDeclaringClass());
+        result.fastAdd(e);
+        return result;
+    }
+
+    public static <E extends Enum<E>> TEnumSet<E> of(E e1, E e2) {
+        TEnumSet<E> result = TEnumSet.noneOf(e1.getDeclaringClass());
+        result.fastAdd(e1);
+        result.fastAdd(e2);
+        return result;
+    }
+
+    public static <E extends Enum<E>> TEnumSet<E> of(E e1, E e2, E e3) {
+        TEnumSet<E> result = TEnumSet.noneOf(e1.getDeclaringClass());
+        result.fastAdd(e1);
+        result.fastAdd(e2);
+        result.fastAdd(e3);
+        return result;
+    }
+
+    public static <E extends Enum<E>> TEnumSet<E> of(E e1, E e2, E e3, E e4) {
+        TEnumSet<E> result = TEnumSet.noneOf(e1.getDeclaringClass());
+        result.fastAdd(e1);
+        result.fastAdd(e2);
+        result.fastAdd(e3);
+        result.fastAdd(e4);
+        return result;
+    }
+
+    public static <E extends Enum<E>> TEnumSet<E> of(E e1, E e2, E e3, E e4, E e5) {
+        TEnumSet<E> result = TEnumSet.noneOf(e1.getDeclaringClass());
+        result.fastAdd(e1);
+        result.fastAdd(e2);
+        result.fastAdd(e3);
+        result.fastAdd(e4);
+        result.fastAdd(e5);
+        return result;
+    }
+
+    @SafeVarargs
+    public static <E extends Enum<E>> TEnumSet<E> of(E first, E... rest) {
+        TEnumSet<E> result = TEnumSet.noneOf(first.getDeclaringClass());
+        for (E e : rest) {
+            result.fastAdd(e);
+        }
+        return result;
+    }
+
+    @Override
+    public TEnumSet<E> clone() {
+        return copyOf(this);
+    }
+
+    abstract void fastAdd(E t);
+
+    private static void zeroHighBits(int[] bits, int count) {
+        bits[bits.length - 1] &= (~0) >>> (32 - count % 32);
+    }
+}
diff --git a/classlib/src/main/java/org/teavm/classlib/java/util/TGenericEnumSet.java b/classlib/src/main/java/org/teavm/classlib/java/util/TGenericEnumSet.java
new file mode 100644
index 000000000..b0bfce473
--- /dev/null
+++ b/classlib/src/main/java/org/teavm/classlib/java/util/TGenericEnumSet.java
@@ -0,0 +1,238 @@
+/*
+ *  Copyright 2017 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.
+ */
+package org.teavm.classlib.java.util;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import org.teavm.classlib.java.lang.TClass;
+import org.teavm.platform.Platform;
+
+class TGenericEnumSet<E extends Enum<E>> extends TEnumSet<E> {
+    Class<E> cls;
+    int[] bits;
+
+    TGenericEnumSet(Class<E> cls) {
+        this.cls = cls;
+        int constantCount = getConstants(cls).length;
+        int bitCount = ((constantCount - 1) / 32) + 1;
+        this.bits = new int[bitCount];
+    }
+
+    TGenericEnumSet(Class<E> cls, int[] bits) {
+        this.cls = cls;
+        this.bits = bits;
+    }
+
+    static Enum<?>[] getConstants(Class<?> cls) {
+        return Platform.getEnumConstants(((TClass<?>) (Object) cls).getPlatformClass());
+    }
+
+    @Override
+    public Iterator<E> iterator() {
+        return new Iterator<E>() {
+            int index;
+            int indexToRemove = -1;
+            int count = size();
+
+            @Override
+            public boolean hasNext() {
+                return count > 0;
+            }
+
+            @Override
+            public E next() {
+                if (count == 0) {
+                    throw new NoSuchElementException();
+                }
+                indexToRemove = index;
+                while (true) {
+                    int next = Integer.numberOfTrailingZeros(bits[index / 32] >>> (index % 32));
+                    if (next < 32) {
+                        index += next;
+                        --count;
+                        @SuppressWarnings("unchecked")
+                        E returnValue = (E) getConstants(cls)[index++];
+                        return returnValue;
+                    } else {
+                        index = (index / 32 + 1) * 32;
+                    }
+                }
+            }
+
+            @Override
+            public void remove() {
+                if (indexToRemove < 0) {
+                    throw new IllegalStateException();
+                }
+                int bitNumber = indexToRemove / 32;
+                bits[bitNumber] &= ~(1 << (indexToRemove % 32));
+                indexToRemove = -1;
+            }
+        };
+    }
+
+    @Override
+    public int size() {
+        int result = 0;
+        for (int bit : bits) {
+            result += Integer.bitCount(bit);
+        }
+        return result;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == this) {
+            return true;
+        }
+        if (!(o instanceof TGenericEnumSet)) {
+            return false;
+        }
+        TGenericEnumSet<?> other = (TGenericEnumSet<?>) o;
+        return cls == other.cls && Arrays.equals(bits, other.bits);
+    }
+
+    @Override
+    public int hashCode() {
+        return Arrays.hashCode(bits);
+    }
+
+    @Override
+    public boolean removeAll(Collection<?> c) {
+        if (c instanceof TGenericEnumSet<?>) {
+            TGenericEnumSet<?> other = (TGenericEnumSet<?>) c;
+            if (cls == other.cls) {
+                boolean changed = false;
+                for (int i = 0; i < bits.length; ++i) {
+                    int inv = ~other.bits[i];
+                    if ((bits[i] & inv) != bits[i]) {
+                        changed = true;
+                        bits[i] &= inv;
+                    }
+                }
+                return changed;
+            }
+        }
+        return super.removeAll(c);
+    }
+
+    @Override
+    public boolean contains(Object o) {
+        if (!cls.isInstance(o)) {
+            return false;
+        }
+        int n = ((Enum<?>) o).ordinal();
+        int bitNumber = n / 32;
+        int bit = 1 << (n % 32);
+        return (bits[bitNumber] & bit) != 0;
+    }
+
+    @Override
+    void fastAdd(E t) {
+        int n = t.ordinal();
+        int bitNumber = n / 32;
+        bits[bitNumber] |= 1 << (n % 32);
+    }
+
+    @Override
+    public boolean add(E t) {
+        int n = t.ordinal();
+        int bitNumber = n / 32;
+        int bit = 1 << (n % 32);
+        if ((bits[bitNumber] & bit) == 0) {
+            bits[bitNumber] |= bit;
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    @Override
+    public boolean remove(Object o) {
+        if (!cls.isInstance(o)) {
+            return false;
+        }
+
+        int n = ((Enum<?>) o).ordinal();
+        int bitNumber = n / 32;
+        int bit = 1 << (n % 32);
+        if ((bits[bitNumber] & bit) != 0) {
+            bits[bitNumber] &= ~bit;
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    @Override
+    public boolean containsAll(Collection<?> c) {
+        if (c instanceof TGenericEnumSet<?>) {
+            TGenericEnumSet<?> other = (TGenericEnumSet<?>) c;
+            if (cls == other.cls) {
+                for (int i = 0; i < bits.length; ++i) {
+                    if ((bits[i] | other.bits[i]) != bits[i]) {
+                        return false;
+                    }
+                }
+                return true;
+            }
+        }
+        return super.containsAll(c);
+    }
+
+    @Override
+    public boolean addAll(Collection<? extends E> c) {
+        if (c instanceof TGenericEnumSet<?>) {
+            TGenericEnumSet<?> other = (TGenericEnumSet<?>) c;
+            if (cls == other.cls) {
+                boolean added = false;
+                for (int i = 0; i < bits.length; ++i) {
+                    if ((bits[i] | other.bits[i]) != bits[i]) {
+                        added = true;
+                        bits[i] |= other.bits[i];
+                    }
+                }
+                return added;
+            }
+        }
+        return super.addAll(c);
+    }
+
+    @Override
+    public boolean retainAll(Collection<?> c) {
+        if (c instanceof TGenericEnumSet<?>) {
+            TGenericEnumSet<?> other = (TGenericEnumSet<?>) c;
+            if (cls == other.cls) {
+                boolean changed = false;
+                for (int i = 0; i < bits.length; ++i) {
+                    if ((bits[i] & other.bits[i]) != bits[i]) {
+                        changed = true;
+                        bits[i] &= other.bits[i];
+                    }
+                }
+                return changed;
+            }
+        }
+        return super.retainAll(c);
+    }
+
+    @Override
+    public void clear() {
+        Arrays.fill(bits, 0);
+    }
+}
diff --git a/platform/src/main/java/org/teavm/platform/plugin/PlatformGenerator.java b/platform/src/main/java/org/teavm/platform/plugin/PlatformGenerator.java
index cd84bcde8..990cddd2d 100644
--- a/platform/src/main/java/org/teavm/platform/plugin/PlatformGenerator.java
+++ b/platform/src/main/java/org/teavm/platform/plugin/PlatformGenerator.java
@@ -25,12 +25,7 @@ import org.teavm.backend.javascript.spi.InjectorContext;
 import org.teavm.dependency.DependencyAgent;
 import org.teavm.dependency.DependencyPlugin;
 import org.teavm.dependency.MethodDependency;
-import org.teavm.model.CallLocation;
-import org.teavm.model.ClassReader;
-import org.teavm.model.MethodDescriptor;
-import org.teavm.model.MethodReader;
-import org.teavm.model.MethodReference;
-import org.teavm.model.ValueType;
+import org.teavm.model.*;
 import org.teavm.platform.Platform;
 import org.teavm.platform.PlatformClass;
 import org.teavm.platform.PlatformRunnable;
@@ -201,7 +196,11 @@ public class PlatformGenerator implements Generator, Injector, DependencyPlugin
         writer.append("if").ws().append("(!cls.hasOwnProperty(c))").ws().append("{").indent().softNewLine();
         writer.append("return null;").softNewLine();
         writer.outdent().append("}").softNewLine();
-        writer.append("return cls[c]();").softNewLine();
+        writer.append("if").ws().append("(typeof cls[c]").ws().append("===").ws().append("\"function\")").ws()
+                .append("{").indent().softNewLine();
+        writer.append("cls[c]").ws().append("=").ws().append("cls[c]();").softNewLine();
+        writer.outdent().append("}").softNewLine();
+        writer.append("return cls[c];").softNewLine();
         writer.outdent().append("};").softNewLine();
 
         writer.append("return ").append(selfName).append("(").append(context.getParameterName(1))
diff --git a/tests/src/test/java/org/teavm/classlib/java/util/EnumSetTest.java b/tests/src/test/java/org/teavm/classlib/java/util/EnumSetTest.java
new file mode 100644
index 000000000..b1660edcb
--- /dev/null
+++ b/tests/src/test/java/org/teavm/classlib/java/util/EnumSetTest.java
@@ -0,0 +1,203 @@
+/*
+ *  Copyright 2017 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.
+ */
+package org.teavm.classlib.java.util;
+
+import static org.junit.Assert.*;
+import java.util.*;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.teavm.junit.TeaVMTestRunner;
+
+@RunWith(TeaVMTestRunner.class)
+public class EnumSetTest {
+    @Test
+    public void emptyCreated() {
+        EnumSet<L> set = EnumSet.noneOf(L.class);
+        assertEquals("Size", 0, set.size());
+        assertFalse("Iterator.hasNext must return false", set.iterator().hasNext());
+        assertFalse("Does not contain E1", set.contains(L.E1));
+        assertFalse("Does not contain E36", set.contains(L.E36));
+
+        try {
+            set.iterator().next();
+            fail("Iterator expected to throw exception");
+        } catch (NoSuchElementException e) {
+            // OK
+        }
+    }
+
+    @Test
+    public void allItemsCreated() {
+        EnumSet<L> set = EnumSet.allOf(L.class);
+        assertEquals("Size", 36, set.size());
+        assertTrue("Iterator.hasNext must return true", set.iterator().hasNext());
+        assertEquals("Iterator.next must return E1", L.E1, set.iterator().next());
+        assertTrue("Contains E1", set.contains(L.E1));
+        assertTrue("Contains E36", set.contains(L.E36));
+    }
+
+    @Test
+    public void itemAdded() {
+        EnumSet<L> set = EnumSet.noneOf(L.class);
+        assertTrue("Adding absent E2 must return true", set.add(L.E2));
+        assertEquals("Iterator must return E2", L.E2, set.iterator().next());
+        assertTrue("Set must contain E2", set.contains(L.E2));
+        assertEquals("Size must be 1 after first addition", 1, set.size());
+
+        assertFalse("Adding existing E2 must return false", set.add(L.E2));
+        assertEquals("Iterator must return E2 after repeated addition", L.E2, set.iterator().next());
+        assertTrue("Set must contain E2 after repeated addition", set.contains(L.E2));
+        assertEquals("Size must be 1 after repeated addition", 1, set.size());
+
+        assertTrue("Adding absent E4 must return true", set.add(L.E4));
+        assertTrue("Set must contain E4", set.contains(L.E4));
+        assertEquals("Size must be 2", 2, set.size());
+
+        assertTrue("Adding absent E33 must return true", set.add(L.E33));
+        assertTrue("Set must contain E4", set.contains(L.E33));
+        assertEquals("Size must be 3", 3, set.size());
+    }
+
+    @Test
+    public void iteratorWorks() {
+        EnumSet<L> set = EnumSet.noneOf(L.class);
+        set.add(L.E1);
+        set.add(L.E4);
+        set.add(L.E33);
+        set.add(L.E2);
+
+        List<L> items = new ArrayList<>();
+        Iterator<L> iter = set.iterator();
+        while (iter.hasNext()) {
+            items.add(iter.next());
+        }
+        try {
+            iter.next();
+            fail("Can't call Iterator.next after entire collection got iterated");
+        } catch (NoSuchElementException e) {
+            // OK
+        }
+
+        assertEquals(Arrays.asList(L.E1, L.E2, L.E4, L.E33), items);
+
+        try {
+            set.iterator().remove();
+            fail("Can't call Iterator.remove right after initialization");
+        } catch (IllegalStateException e) {
+            // OK
+        }
+
+        iter = EnumSet.copyOf(set).iterator();
+        iter.next();
+        iter.remove();
+        try {
+            iter.remove();
+            fail("Can't call Iterator.remove right after previous removal");
+        } catch (IllegalStateException e) {
+            // OK
+        }
+
+        iter = set.iterator();
+        iter.next();
+        iter.remove();
+        assertEquals(EnumSet.of(L.E2, L.E4, L.E33), set);
+    }
+
+    @Test
+    public void removeAll() {
+        EnumSet<L> original = EnumSet.of(L.E2, L.E3, L.E5, L.E8, L.E32);
+
+        EnumSet<L> set = original.clone();
+        assertTrue(set.removeAll(EnumSet.of(L.E3, L.E10, L.E32)));
+        assertEquals(EnumSet.of(L.E2, L.E5, L.E8), set);
+
+        set = original.clone();
+        assertFalse(set.removeAll(EnumSet.of(L.E4, L.E33)));
+        assertEquals(original, set);
+    }
+
+    @Test
+    public void contains() {
+        EnumSet<L> set = EnumSet.of(L.E2, L.E3, L.E5, L.E8, L.E32);
+        assertFalse(set.contains(L.E1));
+        assertTrue(set.contains(L.E2));
+        assertTrue(set.contains(L.E3));
+        assertFalse(set.contains(L.E4));
+        assertTrue(set.contains(L.E5));
+        assertTrue(set.contains(L.E8));
+        assertFalse(set.contains(L.E31));
+        assertTrue(set.contains(L.E32));
+        assertFalse(set.contains(L.E33));
+    }
+
+    @Test
+    public void add() {
+        EnumSet<L> set = EnumSet.of(L.E2, L.E4);
+        assertFalse(set.add(L.E2));
+        assertTrue(set.add(L.E3));
+        assertEquals(EnumSet.of(L.E2, L.E3, L.E4), set);
+    }
+
+    @Test
+    public void containsAll() {
+        EnumSet<L> set = EnumSet.of(L.E2, L.E3, L.E5, L.E8, L.E32);
+        assertFalse(set.containsAll(EnumSet.of(L.E1)));
+        assertFalse(set.containsAll(EnumSet.of(L.E1, L.E4)));
+        assertTrue(set.containsAll(EnumSet.of(L.E2)));
+        assertTrue(set.containsAll(EnumSet.of(L.E2, L.E5)));
+        assertFalse(set.containsAll(EnumSet.of(L.E2, L.E4)));
+    }
+
+    @Test
+    public void addAll() {
+        EnumSet<L> set = EnumSet.of(L.E2, L.E4);
+
+        assertTrue(set.addAll(EnumSet.of(L.E2, L.E3)));
+        assertEquals(EnumSet.of(L.E2, L.E3, L.E4), set);
+
+        assertFalse(set.addAll(EnumSet.of(L.E2, L.E4)));
+        assertEquals(EnumSet.of(L.E2, L.E3, L.E4), set);
+
+        assertTrue(set.addAll(EnumSet.of(L.E5, L.E6)));
+        assertEquals(EnumSet.of(L.E2, L.E3, L.E4, L.E5, L.E6), set);
+    }
+
+    @Test
+    public void retainAll() {
+        EnumSet<L> original = EnumSet.of(L.E2, L.E4, L.E5);
+
+        EnumSet<L> set = original.clone();
+        assertTrue(set.retainAll(EnumSet.of(L.E2, L.E4)));
+        assertEquals(EnumSet.of(L.E2, L.E4), set);
+
+        set = original.clone();
+        assertTrue(set.retainAll(EnumSet.of(L.E1, L.E2)));
+        assertEquals(EnumSet.of(L.E2), set);
+
+        set = original.clone();
+        assertTrue(set.retainAll(EnumSet.of(L.E1)));
+        assertEquals(EnumSet.noneOf(L.class), set);
+
+        set = original.clone();
+        assertFalse(set.retainAll(EnumSet.of(L.E2, L.E4, L.E5, L.E6)));
+        assertEquals(original, set);
+    }
+
+    enum L {
+        E1, E2, E3, E4, E5, E6, E7, E8, E9, E10, E11, E12, E13, E14, E15, E16, E17, E18, E19, E20, E21, E22, E23,
+        E24, E25, E26, E27, E28, E29, E30, E31, E32, E33, E34, E35, E36
+    }
+}