diff --git a/devito/passes/iet/definitions.py b/devito/passes/iet/definitions.py
index e4195c95c66..0568e833add 100644
--- a/devito/passes/iet/definitions.py
+++ b/devito/passes/iet/definitions.py
@@ -355,7 +355,9 @@ def place_definitions(self, iet, globs=None, **kwargs):
         includes = set()
         if isinstance(iet, EntryFunction) and globs:
             for i in sorted(globs, key=lambda f: f.name):
-                includes.add(self._alloc_array_on_global_mem(iet, i, storage))
+                v = self._alloc_array_on_global_mem(iet, i, storage)
+                if v:
+                    includes.add(v)
 
         iet, efuncs = self._inject_definitions(iet, storage)
 
diff --git a/devito/symbolics/extended_sympy.py b/devito/symbolics/extended_sympy.py
index 87a56c13b78..161f596a049 100644
--- a/devito/symbolics/extended_sympy.py
+++ b/devito/symbolics/extended_sympy.py
@@ -4,7 +4,7 @@
 
 import numpy as np
 import sympy
-from sympy import Expr, Integer, Function, Number, Tuple, sympify
+from sympy import Expr, Float, Integer, Function, Number, Tuple, sympify
 from sympy.core.decorators import call_highest_priority
 
 from devito.tools import (Pickable, as_tuple, is_integer, float2, float3, float4,  # noqa
@@ -278,14 +278,10 @@ class ListInitializer(sympy.Expr, Pickable):
     def __new__(cls, params):
         args = []
         for p in as_tuple(params):
-            if isinstance(p, str):
-                args.append(Symbol(p))
-            elif is_integer(p):
-                args.append(Integer(p))
-            elif not isinstance(p, Expr):
-                raise ValueError("`params` must be an iterable of Expr or str")
-            else:
-                args.append(p)
+            try:
+                args.append(sympify(p))
+            except sympy.SympifyError:
+                raise ValueError("Illegal param `%s`" % p)
         obj = sympy.Expr.__new__(cls, *args)
         obj.params = tuple(args)
         return obj