diff --git a/FastSurferCNN/reduce_to_aseg.py b/FastSurferCNN/reduce_to_aseg.py
index 74cfd550..c7c3cc69 100644
--- a/FastSurferCNN/reduce_to_aseg.py
+++ b/FastSurferCNN/reduce_to_aseg.py
@@ -168,7 +168,7 @@ def create_mask(aseg_data, dnum, enum):
     return aseg_data
 
 
-def flip_wm_islands(aseg_datanp.ndarray) -> np.ndarray:
+def flip_wm_islands(aseg_data : np.ndarray) -> np.ndarray:
     """
     Flip labels of disconnected white matter islands to the other hemisphere.