diff --git a/cayley_test.go b/cayley_test.go
index b94389a5b..e9410719d 100644
--- a/cayley_test.go
+++ b/cayley_test.go
@@ -348,7 +348,7 @@ func TestQueries(t *testing.T) {
 
 		// TODO(kortschak) Be more rigorous in this result validation.
 		if len(got) != len(test.expect) {
-			t.Errorf("Unexpected number of results, got:%d expect:%d.", len(got), len(test.expect))
+			t.Errorf("Unexpected number of results, got:%d expect:%d on %s.", len(got), len(test.expect), test.message)
 		}
 	}
 }
diff --git a/graph/iterator.go b/graph/iterator.go
index e7c2ad859..3880b80b0 100644
--- a/graph/iterator.go
+++ b/graph/iterator.go
@@ -154,11 +154,14 @@ func Next(it Iterator) (Value, bool) {
 }
 
 // Height is a convienence function to measure the height of an iterator tree.
-func Height(it Iterator) int {
+func Height(it Iterator, until Type) int {
+	if it.Type() == until {
+		return 1
+	}
 	subs := it.SubIterators()
 	maxDepth := 0
 	for _, sub := range subs {
-		h := Height(sub)
+		h := Height(sub, until)
 		if h > maxDepth {
 			maxDepth = h
 		}
diff --git a/graph/iterator/and_iterator_optimize.go b/graph/iterator/and_iterator_optimize.go
index f0adfad82..774904d59 100644
--- a/graph/iterator/and_iterator_optimize.go
+++ b/graph/iterator/and_iterator_optimize.go
@@ -300,7 +300,7 @@ func materializeIts(its []graph.Iterator) []graph.Iterator {
 	for _, it := range its {
 		stats := it.Stats()
 		if stats.Size*stats.NextCost < stats.ContainsCost {
-			if graph.Height(it) > 10 {
+			if graph.Height(it, graph.Materialize) > 10 {
 				out = append(out, NewMaterialize(it))
 				continue
 			}
diff --git a/graph/iterator/materialize_iterator.go b/graph/iterator/materialize_iterator.go
index 4180a0bc2..03360800f 100644
--- a/graph/iterator/materialize_iterator.go
+++ b/graph/iterator/materialize_iterator.go
@@ -73,10 +73,16 @@ func (it *Materialize) TagResults(dst map[string]graph.Value) {
 	if !it.hasRun {
 		return
 	}
+	if it.aborted {
+		it.subIt.TagResults(dst)
+		return
+	}
+	if it.lastIndex > len(it.values) {
+		return
+	}
 	for _, tag := range it.tags.Tags() {
 		dst[tag] = it.Result()
 	}
-
 	for tag, value := range it.values[it.lastIndex].tags {
 		dst[tag] = value
 	}
@@ -154,6 +160,7 @@ func (it *Materialize) Stats() graph.IteratorStats {
 }
 
 func (it *Materialize) Next() (graph.Value, bool) {
+	graph.NextLogIn(it)
 	if !it.hasRun {
 		it.materializeSet()
 	}
@@ -164,14 +171,15 @@ func (it *Materialize) Next() (graph.Value, bool) {
 	lastVal := it.Result()
 	for it.lastIndex < len(it.values) {
 		it.lastIndex++
-		if it.Result() != lastVal {
-			return it.Result(), true
+		if it.Result() != lastVal && it.Result() != nil {
+			return graph.NextLogOut(it, it.Result(), true)
 		}
 	}
-	return nil, false
+	return graph.NextLogOut(it, nil, false)
 }
 
 func (it *Materialize) Contains(v graph.Value) bool {
+	graph.ContainsLogIn(it, v)
 	if !it.hasRun {
 		it.materializeSet()
 	}
@@ -180,9 +188,9 @@ func (it *Materialize) Contains(v graph.Value) bool {
 	}
 	if i, ok := it.containsMap[v]; ok {
 		it.lastIndex = i
-		return true
+		return graph.ContainsLogOut(it, v, true)
 	}
-	return false
+	return graph.ContainsLogOut(it, v, false)
 }
 
 func (it *Materialize) NextResult() bool {