diff --git a/src/droplet_growth/register.py b/src/droplet_growth/register.py
index a3d9b630d303b82faf50ce1f0e1ae45d4a640e65..0203af997db2912745cfbde5cbc8603f5541324e 100644
--- a/src/droplet_growth/register.py
+++ b/src/droplet_growth/register.py
@@ -94,7 +94,7 @@ def align_stack(data_or_path, template16, mask2, plot=False, path_to_save=None,
     return aligned_stack, tvec
 
 
-def align_stack_nd(stack, template16, mask2, path=None, plot=False, binnings=(1,16,2), suffix='.aligned.tif'):
+def align_stack_nd(stack, template16, mask2, path=None, plot=False, binnings=(1,16,2), suffix='.aligned.tif')  -> tuple(np.ndarray, dict):
     '''
     stack should contain two channels: bright field and fluorescence.
     BF will be binned 8 times and registered with template8 (aligned BF).