diff --git a/src/kd.jl b/src/kd.jl
index aa155da..6460823 100644
--- a/src/kd.jl
+++ b/src/kd.jl
@@ -88,6 +88,11 @@ function diameter(bounds::Matrix)
     euclidean(vec(bounds[1,:]), vec(bounds[2,:]))
 end
 
+# Helper function to add a function barrier aorund the closure passed
+# as the by argument. There is significant overhead without the barrier.
+function _partialsort!(perm, mid1, mid2, xs, j)
+    return partialsort!(perm, mid1:mid2, by = i -> xs[i, j])
+end
 
 """
     build_kdtree(xs, perm, bounds, leaf_size_cutoff, leaf_diameter_cutoff, verts)
@@ -185,7 +190,7 @@ function build_kdtree(xs::AbstractMatrix{T},
             offset = -offset + (offset <= 0)
             continue
         end
-        p12 = partialsort!(perm, mid1:mid2, by = i -> xs[i, j])
+        p12 = _partialsort!(perm, mid1, mid2, xs, j)
         if xs[p12[1], j] == xs[p12[2], j]
             @debug "tie! Adjusting offset" xs[p12[1], j] xs[p12[2], j] offset
             # This makes the offset 0, 1, -1, 2, -2, ...