diff --git a/core/descriptor.loader.java/src/org/jetbrains/jet/lang/resolve/java/resolver/JavaPackageFragmentProvider.java b/core/descriptor.loader.java/src/org/jetbrains/jet/lang/resolve/java/resolver/JavaPackageFragmentProvider.java
index f477504c4b3..fee1c4ea0c8 100644
--- a/core/descriptor.loader.java/src/org/jetbrains/jet/lang/resolve/java/resolver/JavaPackageFragmentProvider.java
+++ b/core/descriptor.loader.java/src/org/jetbrains/jet/lang/resolve/java/resolver/JavaPackageFragmentProvider.java
@@ -18,6 +18,7 @@ package org.jetbrains.jet.lang.resolve.java.resolver;
 
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.ReadOnly;
 import org.jetbrains.jet.lang.descriptors.ModuleDescriptor;
 import org.jetbrains.jet.lang.descriptors.PackageFragmentProvider;
 import org.jetbrains.jet.lang.resolve.java.JavaDescriptorResolver;
@@ -35,6 +36,7 @@ public interface JavaPackageFragmentProvider extends PackageFragmentProvider {
     JavaPackageFragmentDescriptor getPackageFragment(@NotNull FqName fqName);
 
     @NotNull
+    @ReadOnly
     Collection<Name> getClassNamesInPackage(@NotNull FqName packageName);
 
     @NotNull
diff --git a/core/descriptors/src/org/jetbrains/jet/lang/descriptors/PackageFragmentProvider.java b/core/descriptors/src/org/jetbrains/jet/lang/descriptors/PackageFragmentProvider.java
index 626547233d5..11104a3041a 100644
--- a/core/descriptors/src/org/jetbrains/jet/lang/descriptors/PackageFragmentProvider.java
+++ b/core/descriptors/src/org/jetbrains/jet/lang/descriptors/PackageFragmentProvider.java
@@ -17,6 +17,7 @@
 package org.jetbrains.jet.lang.descriptors;
 
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.ReadOnly;
 import org.jetbrains.jet.lang.resolve.name.FqName;
 
 import java.util.Collection;
@@ -24,11 +25,13 @@ import java.util.List;
 
 public interface PackageFragmentProvider {
     @NotNull
+    @ReadOnly
     List<PackageFragmentDescriptor> getPackageFragments(@NotNull FqName fqName);
 
     /**
      * @return declared subpackages of {@code fqName}
      */
     @NotNull
+    @ReadOnly
     Collection<FqName> getSubPackagesOf(@NotNull FqName fqName);
 }