diff --git a/core/descriptors/src/org/jetbrains/kotlin/descriptors/PackageFragmentProviderImpl.kt b/core/descriptors/src/org/jetbrains/kotlin/descriptors/PackageFragmentProviderImpl.kt
index 80af978819be5..997d931a82a49 100644
--- a/core/descriptors/src/org/jetbrains/kotlin/descriptors/PackageFragmentProviderImpl.kt
+++ b/core/descriptors/src/org/jetbrains/kotlin/descriptors/PackageFragmentProviderImpl.kt
@@ -19,23 +19,27 @@ package org.jetbrains.kotlin.descriptors
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 
-class PackageFragmentProviderImpl(
-    private val packageFragments: Collection<PackageFragmentDescriptor>
+class PackageFragmentProviderImpl private constructor(
+    private val packageFragmentsByFqName: HashMap<FqName, List<PackageFragmentDescriptor>>
 ) : PackageFragmentProviderOptimized {
+    constructor(packageFragments: Collection<PackageFragmentDescriptor>) : this(
+        packageFragmentsByFqName = packageFragments.groupBy { it.fqName } as HashMap<FqName, List<PackageFragmentDescriptor>>
+    )
+
     override fun collectPackageFragments(fqName: FqName, packageFragments: MutableCollection<PackageFragmentDescriptor>) {
-        this.packageFragments.filterTo(packageFragments) { it.fqName == fqName }
+        packageFragments.addAll(packageFragmentsByFqName.getOrDefault(fqName, listOf()))
     }
 
     override fun isEmpty(fqName: FqName): Boolean =
-        this.packageFragments.none { it.fqName == fqName }
+        packageFragmentsByFqName.getOrDefault(fqName, null) != null
 
     @Deprecated("for usages use #packageFragments(FqName) at final point, for impl use #collectPackageFragments(FqName, MutableCollection<PackageFragmentDescriptor>)")
     override fun getPackageFragments(fqName: FqName): List<PackageFragmentDescriptor> =
-        packageFragments.filter { it.fqName == fqName }
+        packageFragmentsByFqName.getOrDefault(fqName, emptyList())
 
     override fun getSubPackagesOf(fqName: FqName, nameFilter: (Name) -> Boolean): Collection<FqName> =
-        packageFragments.asSequence()
-            .map { it.fqName }
+        packageFragmentsByFqName.values
+            .flatMap { collection -> collection.map { it.fqName } }
             .filter { !it.isRoot && it.parent() == fqName }
             .toList()
 }