diff --git a/src/pyclaw/solution.py b/src/pyclaw/solution.py
index 6a6c8cdc..08d209bd 100755
--- a/src/pyclaw/solution.py
+++ b/src/pyclaw/solution.py
@@ -198,8 +198,6 @@ def is_valid(self):
          - (bool) - True if valid, false otherwise
         """
         return all([state.is_valid() for state in self.states])
-
-
     def __str__(self):
         output = "states:\n"
         # This is information about each of the states
diff --git a/src/pyclaw/state.py b/src/pyclaw/state.py
index eff412f7..ff8b6f56 100755
--- a/src/pyclaw/state.py
+++ b/src/pyclaw/state.py
@@ -187,6 +187,16 @@ def is_valid(self):
             if not self.aux.flags['F_CONTIGUOUS']:
                 logger.debug('aux array is not Fortran contiguous.')
                 valid = False
+        if self.grid.mapc2p is not None and self.aux is None:
+            raise ValueError("Mapped grid requires a capacity function, stored in the aux array, " \
+            "but no aux array is present. Please set state.num_aux to a positive value.")
+        elif self.grid.mapc2p is not None and self.aux is not None:
+            if self.index_capa == -1:
+                raise ValueError("Capacity function index is not set. " \
+                "Please set state.index_capa to the appropriate index in the aux array.")
+            elif self.index_capa < 0 or self.index_capa > self.num_aux -1:
+                raise ValueError("Capacity function index out of range. " \
+                "Please set state.index_capa to the appropriate index in the aux array.")
         return valid
  
     def set_cparam(self,fortran_module):
diff --git a/src/pyclaw/tests/unittests/test_state.py b/src/pyclaw/tests/unittests/test_state.py
new file mode 100644
index 00000000..cb71693c
--- /dev/null
+++ b/src/pyclaw/tests/unittests/test_state.py
@@ -0,0 +1,56 @@
+import pytest
+from pyclaw import State
+import pyclaw
+from clawpack.pyclaw import Patch
+import numpy as np
+from examples.advection_2d_annulus import advection_annulus
+
+class TestState():
+
+    @pytest.fixture
+    def state(self) -> State:
+        r_lower = 0.2
+        r_upper = 1.0
+        m_r = 40
+
+        theta_lower = 0.0
+        theta_upper = np.pi*2.0
+        m_theta = 120
+
+        r     = pyclaw.Dimension(r_lower,r_upper,m_r,name='r')
+        theta = pyclaw.Dimension(theta_lower,theta_upper,m_theta,name='theta')
+        
+        patch = Patch([r, theta])
+        patch.grid.mapc2p = advection_annulus.mapc2p_annulus
+        patch.grid.num_ghost = 2
+        num_eqn = 1
+        state = State(patch,num_eqn)
+
+        advection_annulus.qinit(state)
+
+        dx, dy = state.grid.delta
+        p_corners = state.grid.p_nodes
+        state.aux = advection_annulus.edge_velocities_and_area(p_corners[0],p_corners[1],dx,dy)
+        state.index_capa = 2
+        return state
+
+
+    @pytest.mark.parametrize(("raise_error", "aux_none", "invalid_index_capa"), 
+                             [(False, False, -1), # Valid state
+                              (True, True, -1), # Invalid state: aux is None
+                              (True, False, -1), # Invalid state: index_capa is -1
+                              (True, False, -10)]) # Invalid state: index_capa is out of bounds
+    def test_state_initialization(self, state: State, 
+                                  raise_error: bool, 
+                                  aux_none: bool, 
+                                  invalid_index_capa: int) -> None:
+        if raise_error:
+            if aux_none:
+                state.aux = None
+            elif state.aux is not None:
+                state.index_capa = invalid_index_capa
+            with pytest.raises(ValueError):
+                assert not state.is_valid()
+
+        else:
+            assert state.is_valid()
\ No newline at end of file