diff --git a/main/src/main/scala/sbt/SettingCompletions.scala b/main/src/main/scala/sbt/SettingCompletions.scala
index f3668de79..6b94c4c6b 100644
--- a/main/src/main/scala/sbt/SettingCompletions.scala
+++ b/main/src/main/scala/sbt/SettingCompletions.scala
@@ -27,7 +27,7 @@ private[sbt] object SettingCompletions {
     {
       import extracted._
       val r = relation(extracted.structure, true)
-      val allDefs = r._1s.toSeq
+      val allDefs = Def.flattenLocals(Def.compiled(extracted.structure.settings, true)(structure.delegates, structure.scopeLocal, implicitly[Show[ScopedKey[_]]])).map(_._1)
       val projectScope = Load.projectScope(currentRef)
       def resolve(s: Setting[_]): Seq[Setting[_]] = Load.transformSettings(projectScope, currentRef.build, rootProject, s :: Nil)
       def rescope[T](setting: Setting[T]): Seq[Setting[_]] =
@@ -353,4 +353,4 @@ private[sbt] object SettingCompletions {
     classOf[Long],
     classOf[String]
   )
-}
\ No newline at end of file
+}
diff --git a/util/relation/src/main/scala/sbt/Relation.scala b/util/relation/src/main/scala/sbt/Relation.scala
index dcd38fa90..987aafb14 100644
--- a/util/relation/src/main/scala/sbt/Relation.scala
+++ b/util/relation/src/main/scala/sbt/Relation.scala
@@ -129,7 +129,7 @@ private final class MRelation[A, B](fwd: Map[A, Set[B]], rev: Map[B, Set[A]]) ex
 
   def +(pair: (A, B)) = this + (pair._1, Set(pair._2))
   def +(from: A, to: B) = this + (from, to :: Nil)
-  def +(from: A, to: Traversable[B]) =
+  def +(from: A, to: Traversable[B]) = if (to.isEmpty) this else
     new MRelation(add(fwd, from, to), (rev /: to) { (map, t) => add(map, t, from :: Nil) })
 
   def ++(rs: Traversable[(A, B)]) = ((this: Relation[A, B]) /: rs) { _ + _ }