diff --git a/user/super/com/google/gwt/emul/java/util/stream/Collectors.java b/user/super/com/google/gwt/emul/java/util/stream/Collectors.java
index bc7bd14..751f231 100644
--- a/user/super/com/google/gwt/emul/java/util/stream/Collectors.java
+++ b/user/super/com/google/gwt/emul/java/util/stream/Collectors.java
@@ -93,8 +93,16 @@
       Function<? super T, ? extends K> classifier,
       Supplier<M> mapFactory,
       Collector<? super T, A, D> downstream) {
-    return Collector.<T, Map<K, List<T>>, M>of(
-        LinkedHashMap::new,
+    return groupingBy0(LinkedHashMap::new, classifier, mapFactory, downstream);
+  }
+
+  private static <T, K, D, A, M extends Map<K, D>> Collector<T, ?, M> groupingBy0(
+      Supplier<Map<K, List<T>>> supplier,
+      Function<? super T, ? extends K> classifier,
+      Supplier<M> mapFactory,
+      Collector<? super T, A, D> downstream) {
+    return Collector.of(
+        supplier,
         (m, o) -> {
           K k = classifier.apply(o);
           List<T> l = m.get(k);
@@ -172,13 +180,21 @@
 
   public static <T> Collector<T, ?, Map<Boolean, List<T>>> partitioningBy(
       Predicate<? super T> predicate) {
-    // calling groupBy directly rather than partioningBy so that it can be optimized later
-    return groupingBy(predicate::test);
+    return partitioningBy(predicate, toList());
   }
 
   public static <T, D, A> Collector<T, ?, Map<Boolean, D>> partitioningBy(
       Predicate<? super T> predicate, Collector<? super T, A, D> downstream) {
-    return groupingBy(predicate::test, downstream);
+    return groupingBy0(partitionSupplier(), predicate::test, HashMap::new, downstream);
+  }
+
+  private static <T> Supplier<Map<Boolean, List<T>>> partitionSupplier() {
+    return () -> {
+      Map<Boolean, List<T>> partition = new LinkedHashMap<>();
+      partition.put(false, new ArrayList<>());
+      partition.put(true, new ArrayList<>());
+      return partition;
+    };
   }
 
   public static <T> Collector<T,?,Optional<T>> reducing(BinaryOperator<T> op) {
diff --git a/user/test/com/google/gwt/emultest/java8/util/stream/CollectorsTest.java b/user/test/com/google/gwt/emultest/java8/util/stream/CollectorsTest.java
index 93e1d28..bfafad0 100644
--- a/user/test/com/google/gwt/emultest/java8/util/stream/CollectorsTest.java
+++ b/user/test/com/google/gwt/emultest/java8/util/stream/CollectorsTest.java
@@ -256,18 +256,31 @@
     mapOfLists.put(true, Collections.singletonList(true));
     mapOfLists.put(false, Collections.singletonList(false));
     applyItems(mapOfLists, c1, true, false);
+
     mapOfLists.clear();
+    mapOfLists.put(false, Collections.emptyList());
     mapOfLists.put(true, Arrays.asList(true, true));
     applyItems(mapOfLists, c1, true, true);
+
     mapOfLists.clear();
     mapOfLists.put(false, Arrays.asList(false, false));
+    mapOfLists.put(true, Collections.emptyList());
     applyItems(mapOfLists, c1, false, false);
 
-    assertZeroItemsCollectedAs(Collections.emptyMap(), c1);
-    assertSingleItemCollectedAs(
-        Collections.singletonMap(true, Collections.singletonList(true)), c1, true);
-    assertSingleItemCollectedAs(
-        Collections.singletonMap(false, Collections.singletonList(false)), c1, false);
+    mapOfLists.clear();
+    mapOfLists.put(false, Collections.emptyList());
+    mapOfLists.put(true, Collections.emptyList());
+    assertZeroItemsCollectedAs(mapOfLists, c1);
+
+    mapOfLists.clear();
+    mapOfLists.put(false, Collections.emptyList());
+    mapOfLists.put(true, Collections.singletonList(true));
+    assertSingleItemCollectedAs(mapOfLists, c1, true);
+
+    mapOfLists.clear();
+    mapOfLists.put(false, Collections.singletonList(false));
+    mapOfLists.put(true, Collections.emptyList());
+    assertSingleItemCollectedAs(mapOfLists, c1, false);
 
     Collector<Boolean, ?, Map<Boolean, Set<Boolean>>> c2 =
         partitioningBy(Boolean::valueOf, toSet());
@@ -276,11 +289,15 @@
     mapOfSets.put(true, Collections.singleton(true));
     mapOfSets.put(false, Collections.singleton(false));
     applyItems(mapOfSets, c2, true, false);
+
     mapOfSets.clear();
+    mapOfSets.put(false, Collections.emptySet());
     mapOfSets.put(true, Collections.singleton(true));
     applyItems(mapOfSets, c2, true, true);
+
     mapOfSets.clear();
     mapOfSets.put(false, Collections.singleton(false));
+    mapOfSets.put(true, Collections.emptySet());
     applyItems(mapOfSets, c2, false, false);
   }