diff --git a/java/java-impl/src/com/intellij/openapi/roots/impl/ModulePackageIndexImpl.java b/java/java-impl/src/com/intellij/openapi/roots/impl/ModulePackageIndexImpl.java
index 58fdec099d55..7537971e0931 100644
--- a/java/java-impl/src/com/intellij/openapi/roots/impl/ModulePackageIndexImpl.java
+++ b/java/java-impl/src/com/intellij/openapi/roots/impl/ModulePackageIndexImpl.java
@@ -41,8 +41,16 @@ public final class ModulePackageIndexImpl extends ModulePackageIndex {
     return new FilteredQuery<>(myDirectoryIndex.getFilesByPackageName(packageName), myDirCondition);
   }
 
+  @Override
+  public @Nullable String getPackageName(@NotNull VirtualFile fileOrDir) {
+    return myDirectoryIndex.getPackageName(fileOrDir);
+  }
+
   @Override
   public @Nullable String getPackageNameByDirectory(@NotNull VirtualFile dir) {
+    if (!dir.isDirectory()) {
+      LOG.error(dir.getPresentableUrl() + " is not a directory");
+    }
     return myDirectoryIndex.getPackageName(dir);
   }
 }
diff --git a/java/java-impl/src/com/intellij/packageDependencies/ui/PackagePatternProvider.java b/java/java-impl/src/com/intellij/packageDependencies/ui/PackagePatternProvider.java
index 169b2d5920fe..895592781dab 100644
--- a/java/java-impl/src/com/intellij/packageDependencies/ui/PackagePatternProvider.java
+++ b/java/java-impl/src/com/intellij/packageDependencies/ui/PackagePatternProvider.java
@@ -77,8 +77,7 @@ public final class PackagePatternProvider extends PatternDialectProvider {
       if (element instanceof PsiClassOwner javaFile) {
         final VirtualFile virtualFile = javaFile.getVirtualFile();
         LOG.assertTrue(virtualFile != null);
-        final String packageName =
-          PackageIndex.getInstance(element.getProject()).getPackageNameByDirectory(virtualFile.getParent());
+        final String packageName = PackageIndex.getInstance(element.getProject()).getPackageName(virtualFile);
         final String name = virtualFile.getNameWithoutExtension();
         if (!PsiNameHelper.getInstance(element.getProject()).isIdentifier(name)) return null;
         qName = StringUtil.getQualifiedName(packageName, name);
diff --git a/java/java-impl/src/com/intellij/packageDependencies/ui/TreeModelBuilder.java b/java/java-impl/src/com/intellij/packageDependencies/ui/TreeModelBuilder.java
index f86601a80c4d..c757b185fe66 100644
--- a/java/java-impl/src/com/intellij/packageDependencies/ui/TreeModelBuilder.java
+++ b/java/java-impl/src/com/intellij/packageDependencies/ui/TreeModelBuilder.java
@@ -279,10 +279,8 @@ public class TreeModelBuilder {
 
   public @Nullable PackageDependenciesNode getFileParentNode(VirtualFile vFile) {
     LOG.assertTrue(vFile != null);
-    final VirtualFile containingDirectory = vFile.getParent();
-    LOG.assertTrue(containingDirectory != null);
     PsiPackage aPackage = null;
-    final String packageName = PackageIndex.getInstance(myProject).getPackageNameByDirectory(containingDirectory);
+    final String packageName = PackageIndex.getInstance(myProject).getPackageName(vFile);
     if (packageName != null) {
       aPackage = myJavaPsiFacade.findPackage(packageName);
     }
diff --git a/java/java-impl/src/com/intellij/psi/search/scope/packageSet/PatternPackageSet.java b/java/java-impl/src/com/intellij/psi/search/scope/packageSet/PatternPackageSet.java
index 99d1815dd56d..4f8d448a71d2 100644
--- a/java/java-impl/src/com/intellij/psi/search/scope/packageSet/PatternPackageSet.java
+++ b/java/java-impl/src/com/intellij/psi/search/scope/packageSet/PatternPackageSet.java
@@ -77,9 +77,8 @@ public class PatternPackageSet extends PatternBasedPackageSet {
   }
 
   private static String getPackageName(@NotNull VirtualFile file, @NotNull Project project) {
-    VirtualFile dir = file.isDirectory() ? file : file.getParent();
-    if (dir == null) return null;
-    return StringUtil.getQualifiedName(PackageIndex.getInstance(project).getPackageNameByDirectory(dir), file.getNameWithoutExtension());
+    String name = PackageIndex.getInstance(project).getPackageName(file);
+    return name == null ? null : StringUtil.getQualifiedName(name, file.getNameWithoutExtension());
   }
 
   @Override
diff --git a/java/java-indexing-impl/src/com/intellij/openapi/roots/impl/ProjectPackageIndexImpl.java b/java/java-indexing-impl/src/com/intellij/openapi/roots/impl/ProjectPackageIndexImpl.java
index de80e2cb66ca..7cd06b258b8d 100644
--- a/java/java-indexing-impl/src/com/intellij/openapi/roots/impl/ProjectPackageIndexImpl.java
+++ b/java/java-indexing-impl/src/com/intellij/openapi/roots/impl/ProjectPackageIndexImpl.java
@@ -1,6 +1,7 @@
 // Copyright 2000-2024 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package com.intellij.openapi.roots.impl;
 
+import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.roots.PackageIndex;
 import com.intellij.openapi.util.NlsSafe;
@@ -13,6 +14,8 @@ import org.jetbrains.annotations.Nullable;
 
 @ApiStatus.Internal
 public final class ProjectPackageIndexImpl extends PackageIndex {
+  private static final Logger LOG = Logger.getInstance(ProjectPackageIndexImpl.class);
+  
   private final DirectoryIndex myDirectoryIndex;
 
   @ApiStatus.Internal
@@ -36,8 +39,16 @@ public final class ProjectPackageIndexImpl extends PackageIndex {
     return myDirectoryIndex.getDirectoriesByPackageName(packageName, includeLibrarySources);
   }
 
+  @Override
+  public @Nullable String getPackageName(@NotNull VirtualFile fileOrDir) {
+    return myDirectoryIndex.getPackageName(fileOrDir);
+  }
+
   @Override
   public @Nullable String getPackageNameByDirectory(@NotNull VirtualFile dir) {
+    if (!dir.isDirectory()) {
+      LOG.error(dir.getPresentableUrl() + " is not a directory");
+    }
     return myDirectoryIndex.getPackageName(dir);
   }
 }
diff --git a/java/java-psi-api/src/com/intellij/openapi/roots/PackageIndex.java b/java/java-psi-api/src/com/intellij/openapi/roots/PackageIndex.java
index ebd758abe97f..9e3579cd883d 100644
--- a/java/java-psi-api/src/com/intellij/openapi/roots/PackageIndex.java
+++ b/java/java-psi-api/src/com/intellij/openapi/roots/PackageIndex.java
@@ -68,10 +68,24 @@ public abstract class PackageIndex {
   public abstract @NotNull Query<VirtualFile> getDirsByPackageName(@NotNull @NlsSafe String packageName, boolean includeLibrarySources);
 
   /**
-   * Returns the name of the package corresponding to the specified directory or a specific file if the file is a single-file root.
+   * Returns the name of the package corresponding to the specified directory or a specific file, including the files 
+   * that are single file source roots.
    *
-   * @return the package name, or null if the supplied directory does not correspond to any package, 
-   * or the supplied file is not a single-file root.
+   * @return the package name, or null if the supplied directory or file does not correspond to any package.
+   */
+  public @Nullable String getPackageName(@NotNull VirtualFile fileOrDir) {
+    if (fileOrDir.isDirectory()) {
+      return getPackageNameByDirectory(fileOrDir);
+    }
+    VirtualFile parent = fileOrDir.getParent();
+    return parent == null || !parent.isDirectory() ? null : getPackageNameByDirectory(parent);
+  }
+
+  /**
+   * Returns the name of the package corresponding to the specified directory.
+   * Prefer using {@link #getPackageName(VirtualFile)} if single-file source roots are possible.
+   *
+   * @return the package name, or null if the supplied directory does not correspond to any package.
    */
   public abstract @Nullable String getPackageNameByDirectory(@NotNull VirtualFile dir);
 }
diff --git a/java/java-tests/testSrc/com/intellij/java/psi/resolve/SingleFileRootResolveTest.java b/java/java-tests/testSrc/com/intellij/java/psi/resolve/SingleFileRootResolveTest.java
index a7315a0a49d0..539ca985a6f5 100644
--- a/java/java-tests/testSrc/com/intellij/java/psi/resolve/SingleFileRootResolveTest.java
+++ b/java/java-tests/testSrc/com/intellij/java/psi/resolve/SingleFileRootResolveTest.java
@@ -71,7 +71,7 @@ public final class SingleFileRootResolveTest extends LightJavaCodeInsightFixture
     PsiClass aClass = JavaPsiFacade.getInstance(getProject()).findClass("com.example.A", GlobalSearchScope.projectScope(getProject()));
     assertNotNull(aClass);
     // Works for single-file roots as well
-    String pkg = PackageIndex.getInstance(getProject()).getPackageNameByDirectory(aClass.getContainingFile().getVirtualFile());
+    String pkg = PackageIndex.getInstance(getProject()).getPackageName(aClass.getContainingFile().getVirtualFile());
     assertEquals("com.example", pkg);
   }
   
diff --git a/platform/platform-impl/src/com/intellij/ide/lightEdit/project/LightEditDirectoryIndex.java b/platform/platform-impl/src/com/intellij/ide/lightEdit/project/LightEditDirectoryIndex.java
index 43df0c00c880..5cd23e2380e9 100644
--- a/platform/platform-impl/src/com/intellij/ide/lightEdit/project/LightEditDirectoryIndex.java
+++ b/platform/platform-impl/src/com/intellij/ide/lightEdit/project/LightEditDirectoryIndex.java
@@ -21,7 +21,7 @@ final class LightEditDirectoryIndex extends DirectoryIndex {
   }
 
   @Override
-  public @Nullable String getPackageName(@NotNull VirtualFile dir) {
+  public @Nullable String getPackageName(@NotNull VirtualFile fileOrDir) {
     return null;
   }
 
diff --git a/platform/projectModel-impl/src/com/intellij/openapi/roots/impl/DirectoryIndex.java b/platform/projectModel-impl/src/com/intellij/openapi/roots/impl/DirectoryIndex.java
index 7edf80b5213c..2c938f188cb0 100644
--- a/platform/projectModel-impl/src/com/intellij/openapi/roots/impl/DirectoryIndex.java
+++ b/platform/projectModel-impl/src/com/intellij/openapi/roots/impl/DirectoryIndex.java
@@ -45,7 +45,7 @@ public abstract class DirectoryIndex {
     return getDirectoriesByPackageName(packageName, true).filtering(scope::contains);
   }
 
-  public abstract @Nullable String getPackageName(@NotNull VirtualFile dir);
+  public abstract @Nullable String getPackageName(@NotNull VirtualFile fileOrDir);
 
   public abstract @NotNull List<OrderEntry> getOrderEntries(@NotNull VirtualFile fileOrDir);
 
diff --git a/platform/projectModel-impl/src/com/intellij/openapi/roots/impl/DirectoryIndexImpl.java b/platform/projectModel-impl/src/com/intellij/openapi/roots/impl/DirectoryIndexImpl.java
index 01136d137f8a..139a26645f12 100644
--- a/platform/projectModel-impl/src/com/intellij/openapi/roots/impl/DirectoryIndexImpl.java
+++ b/platform/projectModel-impl/src/com/intellij/openapi/roots/impl/DirectoryIndexImpl.java
@@ -122,9 +122,9 @@ public final class DirectoryIndexImpl extends DirectoryIndex implements Disposab
   }
 
   @Override
-  public String getPackageName(@NotNull VirtualFile dir) {
+  public String getPackageName(@NotNull VirtualFile fileOrDir) {
     checkAvailability();
-    return myWorkspaceFileIndex.getPackageName(dir);
+    return myWorkspaceFileIndex.getPackageName(fileOrDir);
   }
 
   @Override
diff --git a/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/EmptyWorkspaceFileIndexData.kt b/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/EmptyWorkspaceFileIndexData.kt
index 25bf0c7cf3c6..a8719d0eaa4a 100644
--- a/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/EmptyWorkspaceFileIndexData.kt
+++ b/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/EmptyWorkspaceFileIndexData.kt
@@ -35,7 +35,7 @@ class EmptyWorkspaceFileIndexData private constructor(private val debugName: Str
   override fun markDirty(entityPointers: Collection<EntityPointer<WorkspaceEntity>>, filesToInvalidate: Collection<VirtualFile>) {}
   override fun onEntitiesChanged(event: VersionedStorageChange, storageKind: EntityStorageKind) {}
   override fun updateDirtyEntities() {}
-  override fun getPackageName(dir: VirtualFile): String? = null
+  override fun getPackageName(dirOrFile: VirtualFile): String? = null
   override fun getDirectoriesByPackageName(packageName: String, includeLibrarySources: Boolean): Query<VirtualFile> = EmptyQuery.getEmptyQuery()
   override fun getFilesByPackageName(packageName: String): Query<VirtualFile> = EmptyQuery.getEmptyQuery()
   override fun resetCustomContributors() {}
diff --git a/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexData.kt b/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexData.kt
index 6b5aa11b978e..1d95d68ad1fb 100644
--- a/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexData.kt
+++ b/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexData.kt
@@ -50,10 +50,10 @@ interface WorkspaceFileIndexData {
   fun analyzeVfsChanges(events: List<VFileEvent>): VfsChangeApplier?
 
   /**
-   * Returns package name for [directory] if it's located under source root or classes root of Java library, or `null` otherwise.
+   * Returns package name for [dirOrFile] if it's located under source root or classes root of Java library, or `null` otherwise.
    * This is an internal function, plugins must use [com.intellij.openapi.roots.PackageIndex.getPackageNameByDirectory] instead.
    */
-  fun getPackageName(dir: VirtualFile): String?
+  fun getPackageName(dirOrFile: VirtualFile): String?
 
   /**
    * Returns a query producing directories which correspond to [packageName].
diff --git a/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexDataImpl.kt b/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexDataImpl.kt
index 227b2e8a1bbe..94f81dd9f736 100644
--- a/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexDataImpl.kt
+++ b/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexDataImpl.kt
@@ -380,14 +380,17 @@ internal class WorkspaceFileIndexDataImpl(
     return root
   }
 
-  override fun getPackageName(dir: VirtualFile): String? = WorkspaceFileIndexDataMetrics.getPackageNameTimeNanosec.addMeasuredTime {
-    val fileSet = when (val info = getFileInfo(dir, true, true, true, true, true, true)) {
+  override fun getPackageName(dirOrFile: VirtualFile): String? = WorkspaceFileIndexDataMetrics.getPackageNameTimeNanosec.addMeasuredTime {
+    val fileSet = when (val info = getFileInfo(dirOrFile, true, true, true, true, true, true)) {
                     is WorkspaceFileSetWithCustomData<*> -> info.takeIf { it.data is JvmPackageRootDataInternal }
                     is MultipleWorkspaceFileSets -> info.find(JvmPackageRootDataInternal::class.java)
                     else -> null
                   } ?: return@addMeasuredTime null
 
     val packagePrefix = (fileSet.data as JvmPackageRootDataInternal).packagePrefix
+    if (!fileSet.root.isDirectory) return@addMeasuredTime packagePrefix
+    val dir = if (dirOrFile.isDirectory) dirOrFile else dirOrFile.parent
+    if (!dir.isDirectory) return@addMeasuredTime null
     val packageName = VfsUtilCore.getRelativePath(dir, correctRoot(fileSet.root, dir), '.') 
                       ?: error("${dir.presentableUrl} is not under ${fileSet.root.presentableUrl}")
     return@addMeasuredTime when {
diff --git a/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexEx.kt b/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexEx.kt
index dadb906e209c..a7325ce97e82 100644
--- a/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexEx.kt
+++ b/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexEx.kt
@@ -81,10 +81,11 @@ interface WorkspaceFileIndexEx : WorkspaceFileIndex {
                                        fileSetFilter: (WorkspaceFileSetWithCustomData<*>) -> Boolean): Boolean
 
   /**
-   * Returns package name for [directory] if it's located under source root or classes root of Java library, or `null` otherwise.
+   * Returns package name for [fileOrDir] if it's a single file source root, or a directory located under source root or 
+   * classes root of a Java library. Returns `null` otherwise.
    * This is an internal function, plugins must use [com.intellij.openapi.roots.PackageIndex.getPackageNameByDirectory] instead.
    */
-  fun getPackageName(directory: VirtualFile): String?
+  fun getPackageName(fileOrDir: VirtualFile): String?
 
   /**
    * Returns a query producing directories which correspond to [packageName]. 
diff --git a/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexImpl.kt b/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexImpl.kt
index 67c5e957c779..76b9e5bc0ec7 100644
--- a/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexImpl.kt
+++ b/platform/projectModel-impl/src/com/intellij/workspaceModel/core/fileIndex/impl/WorkspaceFileIndexImpl.kt
@@ -370,8 +370,8 @@ class WorkspaceFileIndexImpl(private val project: Project) : WorkspaceFileIndexE
     getMainIndexData().visitFileSets(visitor)
   }
 
-  override fun getPackageName(directory: VirtualFile): String? {
-    return getMainIndexData().getPackageName(directory)
+  override fun getPackageName(fileOrDir: VirtualFile): String? {
+    return getMainIndexData().getPackageName(fileOrDir)
   }
 
   override fun getDirectoriesByPackageName(packageName: String, includeLibrarySources: Boolean): Query<VirtualFile> {
diff --git a/plugins/search-everywhere-ml/ranking/java/src/com/intellij/searchEverywhereMl/ranking/java/features/SearchEverywhereJavaPsiElementFeatureProvider.kt b/plugins/search-everywhere-ml/ranking/java/src/com/intellij/searchEverywhereMl/ranking/java/features/SearchEverywhereJavaPsiElementFeatureProvider.kt
index 9d3de80e43f7..faf37f9ce1d2 100644
--- a/plugins/search-everywhere-ml/ranking/java/src/com/intellij/searchEverywhereMl/ranking/java/features/SearchEverywhereJavaPsiElementFeatureProvider.kt
+++ b/plugins/search-everywhere-ml/ranking/java/src/com/intellij/searchEverywhereMl/ranking/java/features/SearchEverywhereJavaPsiElementFeatureProvider.kt
@@ -61,11 +61,8 @@ internal class SearchEverywhereJavaPsiElementFeatureProvider : SearchEverywhereE
       val packageIndex = PackageIndex.getInstance(project)
 
       // Parents of some files may still not be directories
-      val openedFileDirectory = openedFile.parent?.takeIf { it.isDirectory }
-      val foundFileDirectory = if (file.isDirectory) file else file.parent?.takeIf { it.isDirectory }
-
-      val openedFilePackageName = openedFileDirectory?.let { packageIndex.getPackageNameByDirectory(it) }
-      val foundFilePackageName = foundFileDirectory?.let { packageIndex.getPackageNameByDirectory(it) }
+      val openedFilePackageName = packageIndex.getPackageName(openedFile)
+      val foundFilePackageName = packageIndex.getPackageName(file)
 
       Pair(openedFilePackageName, foundFilePackageName)
     }.run {