diff --git a/d3-array/d3-array-tests.ts b/d3-array/d3-array-tests.ts
index 7183320b71..26ef2d3ef5 100644
--- a/d3-array/d3-array-tests.ts
+++ b/d3-array/d3-array-tests.ts
@@ -154,7 +154,7 @@ extentNum = d3Array.extent(numbersArray);
 extentStr = d3Array.extent(stringyNumbersArray);
 extentNumeric = d3Array.extent(numericArray);
 extentDate = d3Array.extent(dateArray);
-extentMixed = d3Array.extent([new NumCoercible(10), 13, '12', true]);
+extentMixed = d3Array.extent<NumCoercible>([new NumCoercible(10), 13, '12', true]);
 
 // with accessors