diff --git a/rover/rover.py b/rover/rover.py
index 56d4453..e49843e 100644
--- a/rover/rover.py
+++ b/rover/rover.py
@@ -2,7 +2,7 @@ import enum
 from copy import deepcopy
 from typing import List
 
-from pydantic import BaseModel, validator
+from pydantic import BaseModel, root_validator, validator
 
 
 class Vector(BaseModel):
@@ -41,6 +41,19 @@ class Rover(BaseModel):
     planet_size: Vector = Vector(x=100, y=100)
     dir: Direction = Direction.NORTH
 
+    @root_validator()
+    def _validate_pos(cls, values) -> None:
+        pos, planet_size = values.get("pos"), values.get("planet_size")
+        if pos.x > planet_size.x:
+            raise ValueError(
+                f"pos.x (= {pos.x}) should be under planet_size.x (= {planet_size.x})"
+            )
+        if pos.y > planet_size.y:
+            raise ValueError(
+                f"pos.y (= {pos.y}) should be under planet_size.y (= {planet_size.y})"
+            )
+        return values
+
     def _translate(self, value):
         if self.dir == Direction.NORTH:
             self.pos.y += value
diff --git a/rover/test_rover.py b/rover/test_rover.py
index 9b92447..2264006 100644
--- a/rover/test_rover.py
+++ b/rover/test_rover.py
@@ -237,3 +237,13 @@ def test_rover_negative_x_construction():
 def test_rover_negative_y_construction():
     with pytest.raises(ValidationError):
         _ = Rover(pos=Vector(x=0, y=-1))
+
+
+def test_rover_oversize_x_construction():
+    with pytest.raises(ValidationError):
+        _ = Rover(pos=Vector(x=11, y=0), planet_size=Vector(x=10, y=10))
+
+
+def test_rover_oversize_y_construction():
+    with pytest.raises(ValidationError):
+        _ = Rover(pos=Vector(x=0, y=11), planet_size=Vector(x=10, y=10))