diff --git a/lib/pure/algorithm.nim b/lib/pure/algorithm.nim
index 68960e2e8d..f7ccb92348 100644
--- a/lib/pure/algorithm.nim
+++ b/lib/pure/algorithm.nim
@@ -40,8 +40,8 @@ proc reverse*[T](a: var openArray[T]) =
 proc reversed*[T](a: openArray[T], first, last: Natural): seq[T] =
   ## returns the reverse of the array `a[first..last]`.
   result = newSeq[T](last - first + 1)
-  var x = first
-  var y = last
+  var x = first.int
+  var y = last.int
   while x <= last:
     result[x] = a[y]
     dec(y)