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
@@ -362,7 +362,9 @@
      * Instance Variables                                                      *
      *                                                                         *
      **************************************************************************/
-    
+
+    private boolean ignoreSortUpdate = false;
+
     private boolean expandedDescendentCountDirty = true;
 
     // The ObservableList containing all children belonging to this TreeItem.
@@ -632,8 +634,15 @@
         // we need to check if this TreeItem needs to have its children sorted.
         // There are two different ways that this could be possible.
         if (children.isEmpty()) return children;
-        
-        checkSortState();
+
+        // checkSortState should in almost all instances be called, but there
+        // are situations where checking the sort state will result in
+        // unwanted permutation events being fired (if a sort is applied). To
+        // avoid this (which resolves RT-37593), we set the ignoreSortUpdate
+        // to true (and of course, we're careful to set it back to false again)
+        if (!ignoreSortUpdate) {
+            checkSortState();
+        }
         
         return children;
     }
@@ -875,17 +884,19 @@
         }
         return expandedDescendentCount;
     }
-    
+
     private void updateExpandedDescendentCount(boolean reset) {
         previousExpandedDescendentCount = expandedDescendentCount;
         expandedDescendentCount = 1;
-        
+
+        ignoreSortUpdate = true;
         if (!isLeaf() && isExpanded()) {
             for (TreeItem<T> child : getChildren()) {
                 if (child == null) continue;
                 expandedDescendentCount += child.isExpanded() ? child.getExpandedDescendentCount(reset) : 1;
             }
         }
+        ignoreSortUpdate = false;
     }
 
     private void updateChildren(List<? extends TreeItem<T>> added, List<? extends TreeItem<T>> removed) {
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
@@ -3770,4 +3770,43 @@
         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()));
+
+        treeTableView.setShowRoot(false);
+        treeTableView.setRoot(root);
+        treeTableView.getColumns().addAll(nameColumn);
+
+        treeTableView.getSortOrder().add(nameColumn);
+        nameColumn.setSortType(TreeTableColumn.SortType.DESCENDING);
+        sm.select(one);
+
+        // at this point, the 'one' item should be in row 2
+        assertTrue(sm.isSelected(2));
+        assertEquals(one, sm.getSelectedItem());
+
+        two.setExpanded(true);
+
+        // this line would create a NPE
+        VirtualFlowTestUtils.clickOnRow(treeTableView, 4);
+
+        // we should end up with the selection being on index 4, which is the
+        // final location of the 'one' tree item, after sorting and expanding 'two'
+        assertEquals(one, sm.getSelectedItem());
+        assertTrue(debug(), sm.isSelected(4));
+    }
 }