diff --git a/hamilflow/models/discrete/d0/free_particle.py b/hamilflow/models/discrete/d0/free_particle.py
index 8512bd0..2e7e3e8 100644
--- a/hamilflow/models/discrete/d0/free_particle.py
+++ b/hamilflow/models/discrete/d0/free_particle.py
@@ -23,11 +23,11 @@ class FreeParticleIC(BaseModel):
 
     @model_validator(mode="after")
     def check_dimensions_match(self) -> Self:
-        assert (
-            len(self.x0) == len(cast(Sequence, self.v0))
-            if isinstance(self.x0, Sequence)
-            else not isinstance(self.v0, Sequence)
-        )
+        if (x0_seq := isinstance(self.x0, Sequence)) != isinstance(self.v0, Sequence):
+            raise TypeError("x0 and v0 needs both to be scalars or Sequences")
+        elif x0_seq and len(cast(Sequence, self.x0)) != len(cast(Sequence, self.v0)):
+            raise ValueError("Sequences x0 and v0 needs to have the same length")
+
         return self
 
 
diff --git a/tests/test_models/discrete/d0/test_free_particle.py b/tests/test_models/discrete/d0/test_free_particle.py
index b2a6731..574bee0 100644
--- a/tests/test_models/discrete/d0/test_free_particle.py
+++ b/tests/test_models/discrete/d0/test_free_particle.py
@@ -15,9 +15,13 @@ def test_constructor(
     ) -> None:
         assert FreeParticleIC(x0=x0, v0=v0)
 
-    @pytest.mark.parametrize(("x0", "v0"), [(1, (2,)), ((1,), (2, 3))])
-    def test_raise(self, x0: int | Sequence[int], v0: int | Sequence[int]) -> None:
-        with pytest.raises(ValidationError):
+    @pytest.mark.parametrize(
+        ("x0", "v0", "expected"), [(1, (2,), TypeError), ((1,), (2, 3), ValueError)]
+    )
+    def test_raise(
+        self, x0: int | Sequence[int], v0: Sequence[int], expected: type[Exception]
+    ) -> None:
+        with pytest.raises(expected):
             FreeParticleIC(x0=x0, v0=v0)