diff --git a/java/compiler/impl/src/com/intellij/compiler/backwardRefs/CompilerReferenceReader.java b/java/compiler/impl/src/com/intellij/compiler/backwardRefs/CompilerReferenceReader.java
index 2c21dde2bf78..82707ee2b2e7 100644
--- a/java/compiler/impl/src/com/intellij/compiler/backwardRefs/CompilerReferenceReader.java
+++ b/java/compiler/impl/src/com/intellij/compiler/backwardRefs/CompilerReferenceReader.java
@@ -17,6 +17,7 @@ package com.intellij.compiler.backwardRefs;
 
 import com.intellij.compiler.server.BuildManager;
 import com.intellij.openapi.application.ReadAction;
+import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.openapi.fileTypes.FileType;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.util.Couple;
@@ -45,6 +46,8 @@ import java.util.*;
 import static java.util.stream.Collectors.*;
 
 class CompilerReferenceReader {
+  private final static Logger LOG = Logger.getInstance(CompilerReferenceReader.class);
+
   private final CompilerBackwardReferenceIndex myIndex;
 
   private CompilerReferenceReader(File buildDir) throws IOException {
@@ -85,6 +88,7 @@ class CompilerReferenceReader {
 
     GlobalSearchScope effectiveSearchScope = GlobalSearchScope.notScope(dirtyScope).intersectWith(searchScope);
     LanguageLightRefAdapter adapter = CompilerReferenceServiceImpl.findAdapterForFileType(fileType);
+    LOG.assertTrue(adapter != null, "adapter is null for file type: " + fileType);
     Class<? extends LightRef> requiredLightRefClass = searchType.getRequiredClass(adapter);
     Map<VirtualFile, List<LightRef>> candidatesPerFile = candidates
       .stream()
diff --git a/java/compiler/impl/src/com/intellij/compiler/backwardRefs/CompilerReferenceServiceImpl.java b/java/compiler/impl/src/com/intellij/compiler/backwardRefs/CompilerReferenceServiceImpl.java
index 7cf8a437061d..93431408923c 100644
--- a/java/compiler/impl/src/com/intellij/compiler/backwardRefs/CompilerReferenceServiceImpl.java
+++ b/java/compiler/impl/src/com/intellij/compiler/backwardRefs/CompilerReferenceServiceImpl.java
@@ -194,7 +194,7 @@ public class CompilerReferenceServiceImpl extends CompilerReferenceService imple
                                                                                  @NotNull GlobalSearchScope searchScope,
                                                                                  @NotNull FileType searchFileType,
                                                                                  @NotNull CompilerHierarchySearchType searchType) {
-      if (!isServiceEnabledFor(aClass) || searchScope == LibraryScopeCache.getInstance(myProject).getLibrariesOnlyScope()) return null;
+    if (!isServiceEnabledFor(aClass) || searchScope == LibraryScopeCache.getInstance(myProject).getLibrariesOnlyScope()) return null;
 
     Couple<Map<VirtualFile, T[]>> directInheritorsAndCandidates =
       CachedValuesManager.getCachedValue(aClass, () -> CachedValueProvider.Result.create(
@@ -284,6 +284,7 @@ public class CompilerReferenceServiceImpl extends CompilerReferenceService imple
         return null;
       }
       final LanguageLightRefAdapter<?, ?> adapter = findAdapterForFileType(file.getFileType());
+      if (adapter == null) return null;
       final LightRef ref = ReadAction.compute(() -> adapter.asLightUsage(psiElement, myReader.getNameEnumerator()));
       if (ref == null) return null;
       if (place == ElementPlace.LIB && buildHierarchyForLibraryElements) {
@@ -360,13 +361,14 @@ public class CompilerReferenceServiceImpl extends CompilerReferenceService imple
     return myProject;
   }
 
+  @Nullable
   static LanguageLightRefAdapter findAdapterForFileType(@NotNull FileType fileType) {
     for (LanguageLightRefAdapter adapter : LanguageLightRefAdapter.INSTANCES) {
       if (adapter.getFileTypes().contains(fileType)) {
         return adapter;
       }
     }
-    throw new AssertionError("adapter is not found for: " + fileType);
+    return null;
   }
 
   private static void executeOnBuildThread(Runnable compilationFinished) {
diff --git a/java/java-indexing-impl/src/com/intellij/psi/impl/search/JavaDirectInheritorsSearcher.java b/java/java-indexing-impl/src/com/intellij/psi/impl/search/JavaDirectInheritorsSearcher.java
index e267486b576d..cf7ef670c80a 100644
--- a/java/java-indexing-impl/src/com/intellij/psi/impl/search/JavaDirectInheritorsSearcher.java
+++ b/java/java-indexing-impl/src/com/intellij/psi/impl/search/JavaDirectInheritorsSearcher.java
@@ -281,7 +281,7 @@ public class JavaDirectInheritorsSearcher implements QueryExecutor<PsiClass, Dir
     SearchScope scope = parameters.getScope();
     if (!(scope instanceof GlobalSearchScope)) return null;
 
-    PsiClass searchClass = (PsiClass)PsiUtil.preferCompiledElement(parameters.getClassToProcess());
+    PsiClass searchClass = ReadAction.compute(() -> (PsiClass)PsiUtil.preferCompiledElement(parameters.getClassToProcess()));
     final CompilerReferenceService compilerReferenceService = CompilerReferenceService.getInstance(project);
     return compilerReferenceService.getDirectInheritors(searchClass,
                                                         (GlobalSearchScope)useScope,