diff --git a/modules/controls/src/main/java/javafx/scene/control/TreeItem.java b/modules/controls/src/main/java/javafx/scene/control/TreeItem.java
--- a/modules/controls/src/main/java/javafx/scene/control/TreeItem.java
+++ b/modules/controls/src/main/java/javafx/scene/control/TreeItem.java
@@ -880,8 +880,8 @@
         previousExpandedDescendentCount = expandedDescendentCount;
         expandedDescendentCount = 1;
         
-        if (!isLeaf() && isExpanded()) {
-            for (TreeItem<T> child : getChildren()) {
+        if (!isLeaf() && isExpanded() && children != null) {
+            for (TreeItem<T> child : children) {
                 if (child == null) continue;
                 expandedDescendentCount += child.isExpanded() ? child.getExpandedDescendentCount(reset) : 1;
             }
diff --git a/modules/controls/src/test/java/javafx/scene/control/TreeTableViewTest.java b/modules/controls/src/test/java/javafx/scene/control/TreeTableViewTest.java
--- a/modules/controls/src/test/java/javafx/scene/control/TreeTableViewTest.java
+++ b/modules/controls/src/test/java/javafx/scene/control/TreeTableViewTest.java
@@ -61,6 +61,7 @@
 import javafx.scene.control.cell.*;
 import javafx.scene.image.ImageView;
 import javafx.scene.input.KeyCode;
+import javafx.scene.layout.BorderPane;
 import javafx.scene.layout.StackPane;
 import javafx.scene.layout.VBox;
 import javafx.scene.paint.Color;
@@ -3770,4 +3771,34 @@
         assertEquals(1, rt_37538_count);
         sl.dispose();
     }
+
+    @Test public void test_rt_37593() {
+        TreeItem<String> root = new TreeItem<>();
+
+        TreeItem<String> one = new TreeItem<>("one");
+        root.getChildren().add(one);
+
+        TreeItem<String> two = new TreeItem<>("two");
+        two.getChildren().add(new TreeItem<>("childOne"));
+        two.getChildren().add(new TreeItem<>("childTwo"));
+        root.getChildren().add(two);
+
+        root.getChildren().add(new TreeItem<>("three"));
+
+        TreeTableColumn<String, String> nameColumn = new TreeTableColumn<>("name");
+        nameColumn.setCellValueFactory(param -> new ReadOnlyObjectWrapper(param.getValue().getValue()));
+        nameColumn.setPrefWidth(200);
+
+        TreeTableView<String> table = new TreeTableView<>();
+        table.setShowRoot(false);
+        table.setRoot(root);
+        table.getColumns().addAll(nameColumn);
+
+        table.getSortOrder().add(nameColumn);
+        nameColumn.setSortType(TreeTableColumn.SortType.DESCENDING);
+        table.getSelectionModel().select(one);
+        two.setExpanded(true);
+
+        VirtualFlowTestUtils.clickOnRow(table, 4);
+    }
 }