diff --git a/python/tests/conftest.py b/python/tests/conftest.py
index dc4b44a6a..8ff000ca3 100644
--- a/python/tests/conftest.py
+++ b/python/tests/conftest.py
@@ -150,6 +150,7 @@ def set_of_quaternions():
     specials_scatter /= np.linalg.norm(specials_scatter,axis=1).reshape(-1,1)
     specials_scatter[specials_scatter[:,0]<0]*=-1
 
-    return np.array([s for s in specials] + \
-                    [s for s in specials_scatter] + \
-                    [s for s in random_quaternions(n-2*len(specials))])
+    return np.vstack((specials,
+                      specials_scatter,
+                      random_quaternions(n-2*len(specials)),
+                      ))