diff --git a/test/spec/ol/math.test.js b/test/spec/ol/math.test.js
index 60f0ba9d14..96a722f8bd 100644
--- a/test/spec/ol/math.test.js
+++ b/test/spec/ol/math.test.js
@@ -75,7 +75,7 @@ describe('ol.math.log2', function () {
   });
 
   it('returns the correct value at -1', function () {
-    expect(log2(-1)).to.eql(NaN);
+    expect(log2(-1).toString()).to.eql('NaN');
   });
 });