diff --git a/src/reflect/scala/reflect/internal/Trees.scala b/src/reflect/scala/reflect/internal/Trees.scala
index a8f7612400d8..cf6545c7814b 100644
--- a/src/reflect/scala/reflect/internal/Trees.scala
+++ b/src/reflect/scala/reflect/internal/Trees.scala
@@ -1624,7 +1624,7 @@ trait Trees extends api.Trees {
     protected val changedSymbols = mutable.Set.empty[Symbol]
     protected val treeTypes = mutable.Set.empty[Type]
 
-    def change(sym: Symbol) = {
+    def change(sym: Symbol): Unit = {
       if (sym != NoSymbol && sym.owner == oldowner) {
         sym.owner = newowner
         changedSymbols += sym