diff --git a/d3-box/d3-box-tests.ts b/d3-box/d3-box-tests.ts
index acbd928d6f..191962ff13 100644
--- a/d3-box/d3-box-tests.ts
+++ b/d3-box/d3-box-tests.ts
@@ -3,8 +3,8 @@
 
 // Inspired by http://bl.ocks.org/mbostock/4061502
 
-function iqr(k) {
-  return function(d) {
+function iqr(k: number) {
+  return function(d: any) {
     var q1 = d.quartiles[0],
         q3 = d.quartiles[2],
         iqr = (q3 - q1) * k;