diff --git a/xml/dom-impl/src/com/intellij/codeInsight/navigation/NavigationGutterIconBuilder.java b/xml/dom-impl/src/com/intellij/codeInsight/navigation/NavigationGutterIconBuilder.java
index 874492c6a957..c8b22e6e9fcc 100644
--- a/xml/dom-impl/src/com/intellij/codeInsight/navigation/NavigationGutterIconBuilder.java
+++ b/xml/dom-impl/src/com/intellij/codeInsight/navigation/NavigationGutterIconBuilder.java
@@ -323,6 +323,7 @@ public class NavigationGutterIconBuilder<T> {
     final List<SmartPsiElementPointer> list = new ArrayList<>(targets.size());
     for (final T target : targets) {
       for (final PsiElement psiElement : converter.fun(target)) {
+        assert psiElement != null : converter + " returned null element";
         if (elements.add(psiElement) && psiElement.isValid()) {
           list.add(manager.createSmartPsiElementPointer(psiElement));
         }