diff --git a/platform/core-api/src/com/intellij/psi/PsiWalkingState.java b/platform/core-api/src/com/intellij/psi/PsiWalkingState.java
index 6418a0b60804..5068757c437e 100644
--- a/platform/core-api/src/com/intellij/psi/PsiWalkingState.java
+++ b/platform/core-api/src/com/intellij/psi/PsiWalkingState.java
@@ -17,6 +17,7 @@
 package com.intellij.psi;
 
 import com.intellij.openapi.diagnostic.Logger;
+import com.intellij.psi.util.PsiUtilCore;
 import com.intellij.util.WalkingState;
 import org.jetbrains.annotations.NotNull;
 
@@ -30,12 +31,17 @@ public abstract class PsiWalkingState extends WalkingState<PsiElement> {
   private static class PsiTreeGuide implements TreeGuide<PsiElement> {
     @Override
     public PsiElement getNextSibling(@NotNull PsiElement element) {
-      return element.getNextSibling();
+      return checkSanity(element, element.getNextSibling());
+    }
+
+    private static PsiElement checkSanity(PsiElement element, PsiElement sibling) {
+      if (sibling == PsiUtilCore.NULL_PSI_ELEMENT) throw new PsiInvalidElementAccessException(element, "Sibling of "+element+" is NULL_PSI_ELEMENT");
+      return sibling;
     }
 
     @Override
     public PsiElement getPrevSibling(@NotNull PsiElement element) {
-      return element.getPrevSibling();
+      return checkSanity(element, element.getPrevSibling());
     }
 
     @Override