diff --git a/pyopencl/cffi_cl.py b/pyopencl/cffi_cl.py
index 7fe18c5442b21bff7ba3949ffcc23dcbee325938..f238fccdc980812dd5922d86e23c8ecbc7f2e086 100644
--- a/pyopencl/cffi_cl.py
+++ b/pyopencl/cffi_cl.py
@@ -638,6 +638,10 @@ class CommandQueue(_Common):
     def flush(self):
         _handle_error(_lib.command_queue__flush(self.ptr))
 
+# }}}
+
+
+# {{{ memory objects
 
 def _norm_shape_dtype(shape, dtype, order="C", strides=None, name=""):
     dtype = np.dtype(dtype)
@@ -803,6 +807,8 @@ else:
         with Py_buffer.from_object(obj, flags) as buf:
             return _ffi.cast('void*', buf.buf), buf.len, obj
 
+        # }}}
+
 # }}}
 
 
@@ -1049,7 +1055,6 @@ def enqueue_nd_range_kernel(queue, kernel, global_work_size, local_work_size,
     work_dim = len(global_work_size)
 
     if local_work_size is not None:
-        global_size_copied = False
         if g_times_l:
             work_dim = max(work_dim, len(local_work_size))
         elif work_dim != len(local_work_size):
@@ -1059,16 +1064,14 @@ def enqueue_nd_range_kernel(queue, kernel, global_work_size, local_work_size,
 
         if len(local_work_size) < work_dim:
             local_work_size = (local_work_size +
-                               [1] * (work_dim - len(local_work_size)))
+                               (1,) * (work_dim - len(local_work_size)))
         if len(global_work_size) < work_dim:
-            global_size_copied = True
             global_work_size = (global_work_size +
-                                [1] * (work_dim - len(global_work_size)))
+                                (1,) * (work_dim - len(global_work_size)))
         if g_times_l:
-            if not global_size_copied:
-                global_work_size = list(global_work_size)
-            for i in range(work_dim):
-                global_work_size[i] *= local_work_size[i]
+            global_work_size = tuple(
+                    global_work_size[i] * local_work_size[i]
+                    for i in range(work_dim))
 
     if global_work_offset is not None:
         raise NotImplementedError("global_work_offset")