Fix for si-5590.

src/library/scala/collection/mutable/HashTable.scala

@@ -187,7 +187,7 @@ trait HashTable[A, Entry >: Null <: HashEntry[A, Entry]] extends HashTable.HashU
   }
 
   /** Avoid iterator for a 2x faster traversal. */
-  protected final def foreachEntry[C](f: Entry => C) {
+  protected def foreachEntry[C](f: Entry => C) {
     val iterTable = table
     var idx       = lastPopulatedIndex
     var es        = iterTable(idx)

src/library/scala/collection/mutable/LinkedHashMap.scala

@@ -132,6 +132,14 @@ class LinkedHashMap[A, B] extends AbstractMap[A, B]
     }
   }
 
+  protected override def foreachEntry[C](f: Entry => C) {
+    var cur = firstEntry
+    while (cur ne null) {
+      f(cur)
+      cur = cur.later
+    }
+  }
+
   override def clear() {
     clearTable()
     firstEntry = null

test/files/run/t5590.check

@@ -0,0 +1,4 @@
+Map(a -> a, b -> b, c -> c)
+Map(a -> a, b -> b, c -> c)
+Set(a, b, c, d, e)
+Set(a, b, c, d, e)

test/files/run/t5590.scala

@@ -0,0 +1,31 @@
+
+
+
+import java.io._
+import collection._
+
+
+
+object Test {
+
+  def check(obj: AnyRef) {
+    println(obj)
+
+    val bos = new ByteArrayOutputStream()
+    val out = new ObjectOutputStream(bos)
+    out.writeObject(obj)
+    val arr = bos.toByteArray()
+    val in = new ObjectInputStream(new ByteArrayInputStream(arr))
+    val deser = in.readObject()
+
+    println(deser)
+  }
+
+  def main(args: Array[String]) {
+    val lhm = mutable.LinkedHashMap("a" -> "a", "b" -> "b", "c" -> "c")
+    val lhs = mutable.LinkedHashSet("a", "b", "c", "d", "e")
+    check(lhm)
+    check(lhs)
+  }
+
+}