diff --git a/devito/types/dimension.py b/devito/types/dimension.py
index 43865c72f5d..eb0e64eea45 100644
--- a/devito/types/dimension.py
+++ b/devito/types/dimension.py
@@ -586,7 +586,7 @@ def left(cls, name, parent, thickness, local=True):
         return cls(name, parent,
                    left=parent.symbolic_min,
                    right=parent.symbolic_min+lst-1,
-                   thickness=((lst, thickness), (rst, 0)),
+                   thickness=((lst, thickness), (rst, None)),
                    local=local)
 
     @classmethod
@@ -595,7 +595,7 @@ def right(cls, name, parent, thickness, local=True):
         return cls(name, parent,
                    left=parent.symbolic_max-rst+1,
                    right=parent.symbolic_max,
-                   thickness=((lst, 0), (rst, thickness)),
+                   thickness=((lst, None), (rst, thickness)),
                    local=local)
 
     @classmethod
@@ -628,6 +628,18 @@ def local(self):
     def thickness(self):
         return self._thickness
 
+    @property
+    def is_left(self):
+        return self.thickness.right[1] is None
+
+    @property
+    def is_right(self):
+        return self.thickness.left[1] is None
+
+    @property
+    def is_middle(self):
+        return not self.is_left and not self.is_right
+
     @cached_property
     def bound_symbols(self):
         # Add thickness symbols
@@ -701,7 +713,7 @@ def _arg_values(self, interval, grid=None, **kwargs):
         # However, arguments from the user are considered global
         # So overriding the thickness to a nonzero value should not cause
         # boundaries to exist between ranks where they did not before
-        requested_ltkn, requested_rtkn = (
+        r_ltkn, r_rtkn = (
             kwargs.get(k.name, v) for k, v in self.thickness
         )
 
@@ -710,19 +722,22 @@ def _arg_values(self, interval, grid=None, **kwargs):
             if self.local:
                 # dimension is of type ``left``/right`` - compute the 'offset'
                 # and then add 1 to get the appropriate thickness
-                ltkn = grid.distributor.glb_to_loc(self.root, requested_ltkn-1, LEFT)
-                rtkn = grid.distributor.glb_to_loc(self.root, requested_rtkn-1, RIGHT)
-                ltkn = ltkn+1 if ltkn is not None else 0
-                rtkn = rtkn+1 if rtkn is not None else 0
+                if r_ltkn is not None:
+                    ltkn = grid.distributor.glb_to_loc(self.root, r_ltkn-1, LEFT) + 1
+                else:
+                    ltkn = 0
+
+                if r_rtkn is not None:
+                    rtkn = grid.distributor.glb_to_loc(self.root, r_rtkn-1, RIGHT) + 1
+                else:
+                    rtkn = 0
             else:
                 # dimension is of type ``middle``
-                ltkn = grid.distributor.glb_to_loc(self.root, requested_ltkn,
-                                                   LEFT) or 0
-                rtkn = grid.distributor.glb_to_loc(self.root, requested_rtkn,
-                                                   RIGHT) or 0
+                ltkn = grid.distributor.glb_to_loc(self.root, r_ltkn, LEFT) or 0
+                rtkn = grid.distributor.glb_to_loc(self.root, r_rtkn, RIGHT) or 0
         else:
-            ltkn = requested_ltkn
-            rtkn = requested_rtkn
+            ltkn = r_ltkn or 0
+            rtkn = r_rtkn or 0
 
         return {i.name: v for i, v in zip(self._thickness_map, (ltkn, rtkn))}
 
diff --git a/tests/test_dimension.py b/tests/test_dimension.py
index 9d41dddf484..a54e160b385 100644
--- a/tests/test_dimension.py
+++ b/tests/test_dimension.py
@@ -243,6 +243,10 @@ def test_subdim_middle(self, opt):
         xi = SubDimension.middle(name='xi', parent=x,
                                  thickness_left=1,
                                  thickness_right=1)
+        assert xi.is_middle
+        assert not xi.is_left
+        assert not xi.is_right
+
         eqs = [Eq(u.forward, u + 1)]
         eqs = [e.subs(x, xi) for e in eqs]
 
@@ -261,6 +265,8 @@ def test_symbolic_size(self):
         thickness = 4
 
         xleft = SubDimension.left(name='xleft', parent=x, thickness=thickness)
+        assert xleft.is_left
+        assert not xleft.is_middle
         assert xleft.symbolic_size == xleft.thickness.left[0]
 
         xi = SubDimension.middle(name='xi', parent=x,
@@ -289,7 +295,8 @@ def test_bcs(self, opt):
         xi = SubDimension.middle(name='xi', parent=x,
                                  thickness_left=thickness, thickness_right=thickness)
         xright = SubDimension.right(name='xright', parent=x, thickness=thickness)
-
+        assert xright.is_right
+        assert not xright.is_middle
         yi = SubDimension.middle(name='yi', parent=y,
                                  thickness_left=thickness, thickness_right=thickness)