diff --git a/devito/symbolics/extended_sympy.py b/devito/symbolics/extended_sympy.py
index 7ed801d17a..4087bbc72c 100644
--- a/devito/symbolics/extended_sympy.py
+++ b/devito/symbolics/extended_sympy.py
@@ -799,6 +799,14 @@ class UCHAR(Cast):
     _base_typ = 'unsigned char'
 
 
+class UINT(Cast):
+    _base_typ = 'unsigned int'
+
+
+class UINTP(CastStar):
+    base = UINT
+
+
 class LONG(Cast):
     _base_typ = 'long'
 
diff --git a/devito/tools/dtypes_lowering.py b/devito/tools/dtypes_lowering.py
index 4e7908a552..b5b564a4d7 100644
--- a/devito/tools/dtypes_lowering.py
+++ b/devito/tools/dtypes_lowering.py
@@ -138,7 +138,9 @@ def dtype_to_ctype(dtype):
     except KeyError:
         pass
 
-    if issubclass(dtype, ctypes._SimpleCData):
+    if isinstance(dtype, CustomDtype):
+        return dtype
+    elif issubclass(dtype, ctypes._SimpleCData):
         # Bypass np.ctypeslib's normalization rules such as
         # `np.ctypeslib.as_ctypes_type(ctypes.c_void_p) -> ctypes.c_ulong`
         return dtype