diff --git a/library/src/scala/io/Source.scala b/library/src/scala/io/Source.scala
index 35de2a30b06d..b372fc75db9e 100644
--- a/library/src/scala/io/Source.scala
+++ b/library/src/scala/io/Source.scala
@@ -317,7 +317,7 @@ abstract class Source extends Iterator[Char] with Closeable {
     report(pos, msg, out)
   }
 
-  private def spaces(n: Int) = List.fill(n)(' ').mkString
+  private def spaces(n: Int) = " ".repeat(n)
   /**
    *  @param pos the source position (line/column)
    *  @param msg the error message to report