--- old/src/java.base/share/classes/java/util/ArrayList.java	2018-12-18 12:04:06.042258418 +0000
+++ new/src/java.base/share/classes/java/util/ArrayList.java	2018-12-18 12:04:05.826256876 +0000
@@ -176,15 +176,21 @@
      * @throws NullPointerException if the specified collection is null
      */
     public ArrayList(Collection<? extends E> c) {
-        elementData = c.toArray();
-        if ((size = elementData.length) != 0) {
-            // defend against c.toArray (incorrectly) not returning Object[]
-            // (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
-            if (elementData.getClass() != Object[].class)
-                elementData = Arrays.copyOf(elementData, size, Object[].class);
+        if (c instanceof ArrayList) {
+            elementData = new Object[((ArrayList)c).elementData.length];
+            System.arraycopy(((ArrayList)c).elementData, 0, elementData, 0, ((ArrayList)c).elementData.length);
+            size = ((ArrayList)c).size;
         } else {
-            // replace with empty array.
-            this.elementData = EMPTY_ELEMENTDATA;
+            elementData = c.toArray();
+            if ((size = elementData.length) != 0) {
+                // defend against c.toArray (incorrectly) not returning Object[]
+                // (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
+                if (elementData.getClass() != Object[].class)
+                    elementData = Arrays.copyOf(elementData, size, Object[].class);
+            } else {
+                // replace with empty array.
+                this.elementData = EMPTY_ELEMENTDATA;
+            }
         }
     }