diff --git a/xml/impl/src/com/intellij/xml/util/documentation/HtmlDocumentationProvider.java b/xml/impl/src/com/intellij/xml/util/documentation/HtmlDocumentationProvider.java
index 749bfed32dcf..8d7a25aa63ec 100644
--- a/xml/impl/src/com/intellij/xml/util/documentation/HtmlDocumentationProvider.java
+++ b/xml/impl/src/com/intellij/xml/util/documentation/HtmlDocumentationProvider.java
@@ -16,6 +16,8 @@ import com.intellij.openapi.util.ThrowableComputable;
 import com.intellij.openapi.util.text.StringUtil;
 import com.intellij.psi.*;
 import com.intellij.psi.impl.FakePsiElement;
+import com.intellij.psi.impl.source.html.dtd.HtmlAttributeDescriptorImpl;
+import com.intellij.psi.impl.source.html.dtd.HtmlElementDescriptorImpl;
 import com.intellij.psi.impl.source.xml.SchemaPrefix;
 import com.intellij.psi.meta.PsiMetaData;
 import com.intellij.psi.presentation.java.SymbolPresentationUtil;
@@ -254,7 +256,10 @@ public class HtmlDocumentationProvider implements DocumentationProvider, Externa
     if (element != null && LookupManager.getInstance(element.getProject()).getActiveLookup() == null) {
       XmlAttribute attribute = ReadAction.compute(() -> PsiTreeUtil.getParentOfType(element, XmlAttribute.class, true));
       if (attribute != null) {
-        return HtmlCompatibilityData.getAttributeData(attribute.getParent(), attribute.getName());
+        XmlAttributeDescriptor descriptor = attribute.getDescriptor();
+        String name = descriptor instanceof HtmlAttributeDescriptorImpl && !((HtmlAttributeDescriptorImpl)descriptor).isCaseSensitive() ?
+                      StringUtil.toLowerCase(attribute.getName()) : attribute.getName();
+        return HtmlCompatibilityData.getAttributeData(attribute.getParent(), name);
       }
       else if (element.getParent() instanceof XmlTag) {
         return HtmlCompatibilityData.getTagData((XmlTag)element.getParent());
@@ -265,7 +270,10 @@ public class HtmlDocumentationProvider implements DocumentationProvider, Externa
     } else {
       XmlTag tag = ReadAction.compute(() -> PsiTreeUtil.getParentOfType(element, XmlTag.class, true));
       if (tag != null) {
-        return HtmlCompatibilityData.getAttributeData(tag, entity.name);
+        XmlElementDescriptor descriptor = tag.getDescriptor();
+        String name = descriptor instanceof HtmlElementDescriptorImpl && !((HtmlElementDescriptorImpl)descriptor).isCaseSensitive() ?
+                      StringUtil.toLowerCase(entity.name) : entity.name;
+        return HtmlCompatibilityData.getAttributeData(tag, name);
       }
     }
     return null;
diff --git a/xml/xml-psi-impl/src/com/intellij/psi/impl/source/html/dtd/HtmlElementDescriptorImpl.java b/xml/xml-psi-impl/src/com/intellij/psi/impl/source/html/dtd/HtmlElementDescriptorImpl.java
index 7aa6d8e6942a..172232f95688 100644
--- a/xml/xml-psi-impl/src/com/intellij/psi/impl/source/html/dtd/HtmlElementDescriptorImpl.java
+++ b/xml/xml-psi-impl/src/com/intellij/psi/impl/source/html/dtd/HtmlElementDescriptorImpl.java
@@ -224,4 +224,8 @@ public class HtmlElementDescriptorImpl extends BaseXmlElementDescriptorImpl {
   public String toString() {
     return myDelegate.toString();
   }
+
+  public boolean isCaseSensitive() {
+    return myCaseSensitive;
+  }
 }
diff --git a/xml/xml-psi-impl/src/com/intellij/xml/util/documentation/HtmlCompatibilityData.java b/xml/xml-psi-impl/src/com/intellij/xml/util/documentation/HtmlCompatibilityData.java
index 4b366ea9ccb7..f5dcac7c6d38 100644
--- a/xml/xml-psi-impl/src/com/intellij/xml/util/documentation/HtmlCompatibilityData.java
+++ b/xml/xml-psi-impl/src/com/intellij/xml/util/documentation/HtmlCompatibilityData.java
@@ -103,7 +103,7 @@ public class HtmlCompatibilityData {
   public static Map getAttributeData(@Nullable XmlTag tag, String attributeName) {
     Object data = getTagData(tag);
     if (data != null) {
-      Object attributeData = ((Map)data).get(StringUtil.toLowerCase(attributeName));
+      Object attributeData = ((Map)data).get(attributeName);
       if (attributeData != null) return (Map)attributeData;
     }
     if (ourGlobalAttributesCache.get() == null) {