diff --git a/platform/indexing-api/src/com/intellij/util/indexing/IndexableSetContributor.java b/platform/indexing-api/src/com/intellij/util/indexing/IndexableSetContributor.java
index c971855d1a59..5858c2514c58 100644
--- a/platform/indexing-api/src/com/intellij/util/indexing/IndexableSetContributor.java
+++ b/platform/indexing-api/src/com/intellij/util/indexing/IndexableSetContributor.java
@@ -18,7 +18,6 @@ package com.intellij.util.indexing;
 import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.openapi.extensions.ExtensionPointName;
 import com.intellij.openapi.project.Project;
-import com.intellij.openapi.util.Condition;
 import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.util.containers.ContainerUtil;
 import org.jetbrains.annotations.NotNull;
@@ -60,7 +59,7 @@ public abstract class IndexableSetContributor {
    *         the returned set should not contain nulls or invalid files
    */
   @NotNull
-  public abstract Set getAdditionalRootsToIndex();
+  public abstract Set<VirtualFile> getAdditionalRootsToIndex();
 
   @NotNull
   private static Set<VirtualFile> filterOutNulls(@NotNull IndexableSetContributor contributor,