diff --git a/manimlib/scene/scene.py b/manimlib/scene/scene.py
index 79745ca6..7e6b964a 100644
--- a/manimlib/scene/scene.py
+++ b/manimlib/scene/scene.py
@@ -1023,7 +1023,7 @@ class ThreeDScene(Scene):
     default_frame_orientation = (-30, 70)
     always_depth_test = True
 
-    def add(self, *mobjects, set_depth_test: bool = True):
+    def add(self, *mobjects: Mobject, set_depth_test: bool = True):
         for mob in mobjects:
             if set_depth_test and not mob.is_fixed_in_frame() and self.always_depth_test:
                 mob.apply_depth_test()