diff --git a/jdk/src/share/classes/java/util/IdentityHashMap.java b/jdk/src/share/classes/java/util/IdentityHashMap.java
index 8f0a0cd5c76..9ace500ffc4 100644
--- a/jdk/src/share/classes/java/util/IdentityHashMap.java
+++ b/jdk/src/share/classes/java/util/IdentityHashMap.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2006 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2000-2008 Sun Microsystems, Inc.  All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -749,7 +749,6 @@ public class IdentityHashMap<K,V>
             expectedModCount = ++modCount;
             int deletedSlot = lastReturnedIndex;
             lastReturnedIndex = -1;
-            size--;
             // back up index to revisit new contents after deletion
             index = deletedSlot;
             indexValid = false;
@@ -782,6 +781,8 @@ public class IdentityHashMap<K,V>
                 return;
             }
 
+            size--;
+
             Object item;
             for (int i = nextKeyIndex(d, len); (item = tab[i]) != null;
                  i = nextKeyIndex(i, len)) {
diff --git a/jdk/test/java/util/Map/LockStep.java b/jdk/test/java/util/Map/LockStep.java
new file mode 100644
index 00000000000..58b24e27d7b
--- /dev/null
+++ b/jdk/test/java/util/Map/LockStep.java
@@ -0,0 +1,127 @@
+/*
+ * Copyright 2008 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * @test
+ * @bug 6612102
+ * @summary Test Map implementations for mutual compatibility
+ */
+
+import java.util.*;
+import java.util.concurrent.*;
+
+/**
+ * Based on the strange scenario required to reproduce
+ * (coll) IdentityHashMap.iterator().remove() might decrement size twice
+ *
+ * It would be good to add more "Lockstep-style" tests to this file.
+ */
+public class LockStep {
+    void mapsEqual(Map m1, Map m2) {
+        equal(m1, m2);
+        equal(m2, m1);
+        equal(m1.size(), m2.size());
+        equal(m1.isEmpty(), m2.isEmpty());
+        equal(m1.keySet(), m2.keySet());
+        equal(m2.keySet(), m1.keySet());
+    }
+
+    void mapsEqual(List<Map> maps) {
+        Map first = maps.get(0);
+        for (Map map : maps)
+            mapsEqual(first, map);
+    }
+
+    void put(List<Map> maps, Object key, Object val) {
+        for (Map map : maps)
+            map.put(key, val);
+        mapsEqual(maps);
+    }
+
+    void removeLastTwo(List<Map> maps) {
+        Map first = maps.get(0);
+        int size = first.size();
+        Iterator fit = first.keySet().iterator();
+        for (int j = 0; j < size - 2; j++)
+            fit.next();
+        Object x1 = fit.next();
+        Object x2 = fit.next();
+
+        for (Map map : maps) {
+            Iterator it = map.keySet().iterator();
+            while (it.hasNext()) {
+                Object x = it.next();
+                if (x == x1 || x == x2)
+                    it.remove();
+            }
+        }
+        mapsEqual(maps);
+    }
+
+    void remove(Map m, Iterator it) {
+        int size = m.size();
+        it.remove();
+        if (m.size() != size-1)
+            throw new Error(String.format("Incorrect size!%nmap=%s, size=%d%n",
+                                          m.toString(), m.size()));
+    }
+
+    void test(String[] args) throws Throwable {
+        final int iterations = 100;
+        final Random r = new Random();
+
+        for (int i = 0; i < iterations; i++) {
+            List<Map> maps = Arrays.asList(
+                new Map[] {
+                    new IdentityHashMap(11),
+                    new HashMap(16),
+                    new LinkedHashMap(16),
+                    new WeakHashMap(16),
+                    new Hashtable(16),
+                    new TreeMap(),
+                    new ConcurrentHashMap(16),
+                    new ConcurrentSkipListMap() });
+
+            for (int j = 0; j < 10; j++)
+                put(maps, r.nextInt(100), r.nextInt(100));
+            removeLastTwo(maps);
+        }
+    }
+
+    //--------------------- Infrastructure ---------------------------
+    volatile int passed = 0, failed = 0;
+    void pass() {passed++;}
+    void fail() {failed++; Thread.dumpStack();}
+    void fail(String msg) {System.err.println(msg); fail();}
+    void unexpected(Throwable t) {failed++; t.printStackTrace();}
+    void check(boolean cond) {if (cond) pass(); else fail();}
+    void equal(Object x, Object y) {
+        if (x == null ? y == null : x.equals(y)) pass();
+        else fail(x + " not equal to " + y);}
+    public static void main(String[] args) throws Throwable {
+        new LockStep().instanceMain(args);}
+    void instanceMain(String[] args) throws Throwable {
+        try {test(args);} catch (Throwable t) {unexpected(t);}
+        System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
+        if (failed > 0) throw new AssertionError("Some tests failed");}
+}