diff --git a/xml/impl/src/com/intellij/xml/index/XmlNamespaceIndex.java b/xml/impl/src/com/intellij/xml/index/XmlNamespaceIndex.java
index 5a4b2a8bf513..6d681d5d32ff 100644
--- a/xml/impl/src/com/intellij/xml/index/XmlNamespaceIndex.java
+++ b/xml/impl/src/com/intellij/xml/index/XmlNamespaceIndex.java
@@ -160,7 +160,9 @@ public class XmlNamespaceIndex extends XmlIndex<XsdNamespaceBuilder> {
 
     IndexedRelevantResource<String,XsdNamespaceBuilder> resource =
       guessSchema(namespace, tagName, version, ModuleUtilCore.findModuleForPsiElement(file));
-    return resource == null ? null : (XmlFile)file.getManager().findFile(resource.getFile());
+    if (resource == null) return null;
+    PsiFile psiFile = file.getManager().findFile(resource.getFile());
+    return psiFile instanceof XmlFile ? (XmlFile)psiFile : null;
   }
 
   @Nullable