diff --git a/xml/xml-analysis-impl/src/com/intellij/codeInspection/htmlInspections/HtmlUnknownAttributeInspectionBase.java b/xml/xml-analysis-impl/src/com/intellij/codeInspection/htmlInspections/HtmlUnknownAttributeInspectionBase.java
index b9cee0fc11be..24c5ae62af96 100644
--- a/xml/xml-analysis-impl/src/com/intellij/codeInspection/htmlInspections/HtmlUnknownAttributeInspectionBase.java
+++ b/xml/xml-analysis-impl/src/com/intellij/codeInspection/htmlInspections/HtmlUnknownAttributeInspectionBase.java
@@ -118,7 +118,7 @@ public class HtmlUnknownAttributeInspectionBase extends HtmlUnknownElementInspec
     }
   }
 
-  private static ProblemHighlightType addUnknownXmlAttributeQuickFixes(XmlTag tag,
+  private static @NotNull ProblemHighlightType addUnknownXmlAttributeQuickFixes(XmlTag tag,
                                                                        String name,
                                                                        ArrayList<? super LocalQuickFix> quickfixes,
                                                                        ProblemsHolder holder,
diff --git a/xml/xml-analysis-impl/src/com/intellij/codeInspection/htmlInspections/XmlUnknownAttributeQuickFixProvider.java b/xml/xml-analysis-impl/src/com/intellij/codeInspection/htmlInspections/XmlUnknownAttributeQuickFixProvider.java
index d350a0b31d65..042964ac425a 100644
--- a/xml/xml-analysis-impl/src/com/intellij/codeInspection/htmlInspections/XmlUnknownAttributeQuickFixProvider.java
+++ b/xml/xml-analysis-impl/src/com/intellij/codeInspection/htmlInspections/XmlUnknownAttributeQuickFixProvider.java
@@ -9,7 +9,6 @@ import com.intellij.psi.PsiElement;
 import com.intellij.psi.xml.XmlAttribute;
 import com.intellij.psi.xml.XmlTag;
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
 
 import java.util.Collection;
 
@@ -29,7 +28,7 @@ public interface XmlUnknownAttributeQuickFixProvider {
    */
   @NotNull Collection<@NotNull LocalQuickFix> getOrRegisterAttributeFixes(@NotNull XmlTag tag, @NotNull String name, ProblemsHolder holder, boolean isFixRequired);
 
-  default @Nullable ProblemHighlightType getProblemHighlightType(@NotNull PsiElement element) {
+  default @NotNull ProblemHighlightType getProblemHighlightType(@NotNull PsiElement element) {
     return ProblemHighlightType.GENERIC_ERROR_OR_WARNING;
   }
 }