diff --git a/spawning-pool-core/src/test/scala/com/htmlism/spawningpool/combinatorics/FixedLengthCombinatorSpec.scala b/spawning-pool-core/src/test/scala/com/htmlism/spawningpool/combinatorics/FixedLengthCombinatorSpec.scala
index ecaa28f..2aea9d0 100644
--- a/spawning-pool-core/src/test/scala/com/htmlism/spawningpool/combinatorics/FixedLengthCombinatorSpec.scala
+++ b/spawning-pool-core/src/test/scala/com/htmlism/spawningpool/combinatorics/FixedLengthCombinatorSpec.scala
@@ -45,5 +45,6 @@ class FixedTestCombinator(val size: Int) extends FixedLengthCombinator[String] w
 
   def nextUseFirstParent = parents.next()
 
-  override def fill(unused: Int) = List.fill(size)
+  override def fill(unused: Int): String => List[String] =
+    List.fill(size)(_)
 }