diff --git a/processing/post/addOrientations.py b/processing/post/addOrientations.py
index efd4dac24..27cc92b1f 100755
--- a/processing/post/addOrientations.py
+++ b/processing/post/addOrientations.py
@@ -14,21 +14,23 @@ scriptID   = ' '.join([scriptName,damask.version])
 # --------------------------------------------------------------------
 
 def check_Eulers(eulers):
-  if np.any(eulers < 0.0) or np.any(eulers > 2.0*math.pi) or eulers[1] > math.pi:      # Euler angles within valid range?
+  if np.any(eulers < 0.0) or np.any(eulers > 2.0*math.pi) or eulers[1] > math.pi:                   # Euler angles within valid range?
     raise ValueError('Euler angles outside of [0..2π],[0..π],[0..2π].\n{} {} {}.'.format(*eulers))
   return eulers
 
 def check_quaternion(q):
-  if q.q < 0.0:                                                                 # positive first quaternion component?
+  if q[0] < 0.0:                                                                                    # positive first quaternion component?
     raise ValueError('quaternion has negative first component.\n{}'.format(q))
+  if not(np.isclose(np.linalg.norm(q), 1.0)):                                                       # unit quaternion?
+    raise ValueError('quaternion is not of unit length.\n{} {} {} {}'.format(*q))
   return q
  
 def check_matrix(M):
-  if abs(1.0-np.linalg.det(M)) > 1e-8:                                          # proper rotation?
+  if abs(1.0-np.linalg.det(M)) > 1e-8:                                                              # proper rotation?
     raise ValueError('matrix is not a proper rotation.\n{}'.format(M))
   if    abs(np.dot(M[0],M[1]))    > 1e-8 \
      or abs(np.dot(M[1],M[2]))    > 1e-8 \
-     or abs(np.dot(M[2],M[0]))    > 1e-8:                                       # all orthogonal?
+     or abs(np.dot(M[2],M[0]))    > 1e-8:                                                           # all orthogonal?
     raise ValueError('matrix is not orthogonal.\n{}'.format(M))
   return M