diff --git a/xml/impl/src/com/intellij/xml/index/XmlNamespaceIndex.java b/xml/impl/src/com/intellij/xml/index/XmlNamespaceIndex.java
index 6d681d5d32ff..6268ccededad 100644
--- a/xml/impl/src/com/intellij/xml/index/XmlNamespaceIndex.java
+++ b/xml/impl/src/com/intellij/xml/index/XmlNamespaceIndex.java
@@ -17,6 +17,7 @@ package com.intellij.xml.index;
 
 import com.intellij.openapi.module.Module;
 import com.intellij.openapi.module.ModuleUtilCore;
+import com.intellij.openapi.project.DumbService;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.psi.PsiFile;
@@ -158,6 +159,8 @@ public class XmlNamespaceIndex extends XmlIndex<XsdNamespaceBuilder> {
                                     @Nullable final String version,
                                     @NotNull PsiFile file) {
 
+    if (DumbService.isDumb(file.getProject())) return null;
+
     IndexedRelevantResource<String,XsdNamespaceBuilder> resource =
       guessSchema(namespace, tagName, version, ModuleUtilCore.findModuleForPsiElement(file));
     if (resource == null) return null;