diff --git a/aotools/functions/zernike.py b/aotools/functions/zernike.py
index 0eba058..719fafa 100644
--- a/aotools/functions/zernike.py
+++ b/aotools/functions/zernike.py
@@ -1,4 +1,5 @@
 import numpy
+import math
 from . import circle
 
 def phaseFromZernikes(zCoeffs, size, norm="noll", rot=0):
@@ -88,10 +89,10 @@ def zernikeRadialFunc(n, m, r):
     for i in range(0, int((n - m) / 2) + 1):
 
         R += numpy.array(r**(n - 2 * i) * (((-1)**(i)) *
-                         numpy.math.factorial(n - i)) /
-                         (numpy.math.factorial(i) *
-                          numpy.math.factorial(int(0.5 * (n + m) - i)) *
-                          numpy.math.factorial(int(0.5 * (n - m) - i))),
+                         math.factorial(n - i)) /
+                         (math.factorial(i) *
+                          math.factorial(int(0.5 * (n + m) - i)) *
+                          math.factorial(int(0.5 * (n - m) - i))),
                          dtype='float')
     return R
 
diff --git a/test/test_centroiders.py b/test/test_centroiders.py
index 8b066f6..a8fb3ab 100644
--- a/test/test_centroiders.py
+++ b/test/test_centroiders.py
@@ -1,5 +1,6 @@
 from aotools import image_processing
 import numpy
+# from nose.tools import raises
 
 
 def test_centre_of_gravity_single():
@@ -66,3 +67,13 @@ def test_correlation_many():
     com = image_processing.correlation_centroid(im, ref, 0.3)
     assert (com.shape[0] == 2)
     assert(com.shape[1] == 5)
+
+
+# @raises(ValueError)
+# def test_correlation_error():
+#     im = numpy.random.random((10))
+#     ref = numpy.random.random((10, 10))
+#     com = image_processing.correlation_centroid(im, ref, threshold=0.3)
+
+
+