diff --git a/src/tracker/lib.jl b/src/tracker/lib.jl
index 018a25fc..be77634b 100644
--- a/src/tracker/lib.jl
+++ b/src/tracker/lib.jl
@@ -39,10 +39,13 @@ Base.vcat(a::TrackedMatrix, b::TrackedMatrix)  = TrackedArray(Call(vcat, a, b))
 Base.vcat(a::TrackedMatrix, b::AbstractMatrix) = TrackedArray(Call(vcat, a, b))
 Base.vcat(a::AbstractMatrix, b::TrackedMatrix) = TrackedArray(Call(vcat, a, b))
 
-function back(::typeof(vcat), Δ, xs, ys)
+function back(::typeof(vcat), Δ, xs...)
   i = Base.tail(map(_ -> :, size(Δ)))
-  @back(xs, Δ[1:size(xs,1), i...])
-  @back(ys, Δ[size(xs,1)+1:end, i...])
+  start = 0
+  for xsi in xs
+    @back(xsi, Δ[start+1:start+size(xsi,1), i...])
+    start += size(xsi, 1)
+  end
 end
 
 # Reductions