diff --git a/geomdl/BSpline.py b/geomdl/BSpline.py
index 6fdc790c..e8c72c8c 100644
--- a/geomdl/BSpline.py
+++ b/geomdl/BSpline.py
@@ -964,23 +964,13 @@ def __str__(self):
     def convert3d(self):
         """ Converts 2D curve to a 3D curve.
 
+        .. deprecated:: 3.5
+            Use :py:meth:`.add_dimension()`
+
         :return: 3D curve
         :rtype: BSpline.Curve
         """
-        # Modify control points
-        new_ctrlpts = []
-        for point in self._control_points:
-            temp = [point[0], point[1], 0.0]
-            new_ctrlpts.append(temp)
-
-        # Convert to 3D curve
-        ret_val = Curve()
-        ret_val.degree = self.degree
-        ret_val.ctrlpts = new_ctrlpts
-        ret_val.knotvector = self.knotvector
-        ret_val.delta = self.delta
-
-        return ret_val
+        return self.add_dimension()
 
 
 class Surface(Abstract.Surface):
diff --git a/geomdl/NURBS.py b/geomdl/NURBS.py
index a90964d7..7c688078 100644
--- a/geomdl/NURBS.py
+++ b/geomdl/NURBS.py
@@ -242,23 +242,13 @@ def __str__(self):
     def convert3d(self):
         """ Converts 2D curve to a 3D curve.
 
+        .. deprecated:: 3.5
+            Use :py:meth:`.add_dimension()`
+
         :return: 3D curve
         :rtype: NURBS.Curve
         """
-        # Modify weighted control points
-        new_ctrlpts = []
-        for point in self._control_points:
-            temp = [point[0], point[1], 0.0, point[2]]
-            new_ctrlpts.append(temp)
-
-        # Convert to 3D curve
-        ret_val = Curve()
-        ret_val.degree = self.degree
-        ret_val.ctrlpts = new_ctrlpts
-        ret_val.knotvector = self.knotvector
-        ret_val.delta = self.delta
-
-        return ret_val
+        return self.add_dimension()
 
 
 class Surface(BSpline.Surface):