diff --git a/bits/70_besseli.js b/bits/70_besseli.js
index c67f1a9..6d7ab10 100644
--- a/bits/70_besseli.js
+++ b/bits/70_besseli.js
@@ -17,6 +17,7 @@ var besseli/*:BesselF*/ = (function() {
 
   return function besseli(x/*:number*/, n/*:number*/)/*:number*/ {
     n = Math.round(n);
+    if(x < 0) return ((n%2)?-1:1)*besseli(-x, n);
     if(n === 0) return bessel0(x);
     if(n === 1) return bessel1(x);
     if(n < 0) return NaN;