diff --git a/lib/cartopy/crs.py b/lib/cartopy/crs.py
index a39703e87..c24415167 100644
--- a/lib/cartopy/crs.py
+++ b/lib/cartopy/crs.py
@@ -1372,7 +1372,7 @@ def _bbox_and_offset(self, other_plate_carree):
         bbox = [[lon_lower_bound_0, lon_lower_bound_1],
                 [lon_lower_bound_1, lon_lower_bound_0]]
 
-        bbox[1][1] += np.diff(self.x_limits)[0]
+        bbox[1][1] += self.x_limits[1] - self.x_limits[0]
 
         return bbox, lon_0_offset