diff --git a/src/jaxsim/terrain/terrain.py b/src/jaxsim/terrain/terrain.py
index e9161da27..c9b6e7320 100644
--- a/src/jaxsim/terrain/terrain.py
+++ b/src/jaxsim/terrain/terrain.py
@@ -73,7 +73,7 @@ def __eq__(self, other: FlatTerrain) -> bool:
 class PlaneTerrain(FlatTerrain):
 
     plane_normal: tuple[float, float, float] = jax_dataclasses.field(
-        default=(0.0, 0.0, 0.0), kw_only=True
+        default=(0.0, 0.0, 1.0), kw_only=True
     )
 
     @staticmethod