diff --git a/cv_analysis/utils/merging.py b/cv_analysis/utils/merging.py
index 2997939..15f84a6 100644
--- a/cv_analysis/utils/merging.py
+++ b/cv_analysis/utils/merging.py
@@ -6,13 +6,13 @@ from cv_analysis.utils.rectangle import Rectangle
 from cv_analysis.utils.spacial import is_related
 
 
-def connect_related_rectangles(rectangles: List[Rectangle]):
+def connect_related_rectangles(rectangles: List[Rectangle]) -> List[Rectangle]:
     assert isinstance(rectangles, list)
     no_new_merges = make_merger_sentinel()
     return until(no_new_merges, merge_rectangles_once, rectangles)
 
 
-def merge_rectangles_once(rectangles: List[Rectangle]):
+def merge_rectangles_once(rectangles: List[Rectangle]) -> List[Rectangle]:
     for alpha, beta in combinations(rectangles, 2):
         if is_related(alpha, beta):
             rectangles.remove(alpha)
@@ -22,7 +22,7 @@ def merge_rectangles_once(rectangles: List[Rectangle]):
     return rectangles
 
 
-def bounding_rect(alpha: Rectangle, beta: Rectangle):
+def bounding_rect(alpha: Rectangle, beta: Rectangle) -> Rectangle:
     return Rectangle(
         min(alpha.x1, beta.x1),
         min(alpha.y1, beta.y1),