diff --git a/main/src/main/scala/sbt/Load.scala b/main/src/main/scala/sbt/Load.scala
index 0f0e3ff69..57dc4b640 100755
--- a/main/src/main/scala/sbt/Load.scala
+++ b/main/src/main/scala/sbt/Load.scala
@@ -198,10 +198,10 @@ object Load {
     {
       val keys = Index.allKeys(settings)
       val attributeKeys = Index.attributeKeys(data) ++ keys.map(_.key)
-      val scopedKeys = keys ++ data.allKeys((s, k) => ScopedKey(s, k))
+      val scopedKeys = keys ++ data.allKeys((s, k) => ScopedKey(s, k)).toVector
       val projectsMap = projects.mapValues(_.defined.keySet)
-      val keyIndex = KeyIndex(scopedKeys, projectsMap)
-      val aggIndex = KeyIndex.aggregate(scopedKeys, extra(keyIndex), projectsMap)
+      val keyIndex = KeyIndex(scopedKeys.toVector, projectsMap)
+      val aggIndex = KeyIndex.aggregate(scopedKeys.toVector, extra(keyIndex), projectsMap)
       new sbt.StructureIndex(Index.stringToKeyMap(attributeKeys), Index.taskToKeyMap(data), Index.triggers(data), keyIndex, aggIndex)
     }