diff --git a/sphericalpolygon/excess_area.py b/sphericalpolygon/excess_area.py
index c890ac3..6537b49 100644
--- a/sphericalpolygon/excess_area.py
+++ b/sphericalpolygon/excess_area.py
@@ -29,7 +29,7 @@ def polygon_excess(vertices):
         dlon = np.abs(pdlon) 
         
         # If two adjacent vertices are close enough(coincident), do nothing. 
-        if dlon < 1e-6: continue 
+        if dlon < 1e-6 and np.abs(pdlat) < 1e-6: continue 
 
         # Calculate the area of a spherical triangle consisting of sides and north poles  
         if dlon > np.pi: dlon = 2*np.pi - dlon 
@@ -69,4 +69,4 @@ def polygon_area(vertices):
     
     if area > 2*np.pi: area = 4*np.pi - area
 
-    return area
\ No newline at end of file
+    return area