diff --git a/conftest.py b/conftest.py
index edf83799ef..b2d49697fb 100644
--- a/conftest.py
+++ b/conftest.py
@@ -467,11 +467,11 @@ def check_array(array, exp_halo, exp_shape, rotate=False):
 
     shape = []
     for i in array.symbolic_shape:
-        if i.is_Number or i.is_Symbol:
-            shape.append(i)
-        else:
-            assert i.is_Add
+        if i.is_Add:
+            # Ensure it's a plain sympy.Add and not a subclass
             shape.append(Add(*i.args))
+        else:
+            shape.append(i)
 
     if rotate:
         exp_shape = (sum(exp_halo[0]) + 1,) + tuple(exp_shape[1:])
diff --git a/devito/symbolics/extended_sympy.py b/devito/symbolics/extended_sympy.py
index be79fba3a4..46d2c5a43a 100644
--- a/devito/symbolics/extended_sympy.py
+++ b/devito/symbolics/extended_sympy.py
@@ -634,10 +634,10 @@ def __new__(cls, value, step, **kwargs):
         value = sympify(value)
         step = sympify(step)
 
-        if step < 1:
-            raise ValueError("Cannot round up with negative `step`")
         if not is_integer(step):
             raise ValueError("`step` must be an integer")
+        if step < 1:
+            raise ValueError("Cannot round up with negative `step`")
 
         if value.is_number and step.is_number:
             remainder = value % step
diff --git a/devito/types/basic.py b/devito/types/basic.py
index babd3eaf76..e2af17bd97 100644
--- a/devito/types/basic.py
+++ b/devito/types/basic.py
@@ -930,6 +930,8 @@ def __padding_setup_smart__(self, **kwargs):
         else:
             from devito.symbolics import RoundUp  # noqa
             v = RoundUp(snp, mmts) - snp
+            if v.is_Integer:
+                v = int(v)
 
         dpadding = (0, v)
         padding = [(0, 0)]*self.ndim