diff --git a/unittest/python/test_dimensions.py b/unittest/python/test_dimensions.py
index 3ccc354b7f323cca24099d7e919dd7c220333b70..8a7892a952d294c4344dc53faafbc4ac0fafdcfd 100644
--- a/unittest/python/test_dimensions.py
+++ b/unittest/python/test_dimensions.py
@@ -5,6 +5,7 @@ import numpy as np
 
 quat = eigenpy.Quaternion()
 # By default, we convert as numpy.matrix
+eigenpy.switchToNumpyMatrix()
 coeffs_vector = quat.coeffs() 
 assert len(coeffs_vector.shape) == 2