diff --git a/Modules/cjkcodecs/multibytecodec.c b/Modules/cjkcodecs/multibytecodec.c
index 53135ae4aa7968..08b74740bda4bf 100644
--- a/Modules/cjkcodecs/multibytecodec.c
+++ b/Modules/cjkcodecs/multibytecodec.c
@@ -56,6 +56,27 @@ class _multibytecodec.MultibyteStreamWriter "MultibyteStreamWriterObject *" "cli
 /*[clinic end generated code: output=da39a3ee5e6b4b0d input=305a76dfdd24b99c]*/
 #undef clinic_get_state
 
+#define _MultibyteCodec_CAST(op)        ((MultibyteCodec *)(op))
+#define _MultibyteCodecObject_CAST(op)  ((MultibyteCodecObject *)(op))
+
+#define _MultibyteStatefulCodecContext_CAST(op) \
+    ((MultibyteStatefulCodecContext *)(op))
+
+#define _MultibyteStatefulEncoderContext_CAST(op)   \
+    ((MultibyteStatefulEncoderContext *)(op))
+#define _MultibyteStatefulDecoderContext_CAST(op)   \
+    ((MultibyteStatefulDecoderContext *)(op))
+
+#define _MultibyteIncrementalEncoderObject_CAST(op) \
+    ((MultibyteIncrementalEncoderObject *)(op))
+#define _MultibyteIncrementalDecoderObject_CAST(op) \
+    ((MultibyteIncrementalDecoderObject *)(op))
+
+#define _MultibyteStreamReaderObject_CAST(op)   \
+    ((MultibyteStreamReaderObject *)(op))
+#define _MultibyteStreamWriterObject_CAST(op)   \
+    ((MultibyteStreamWriterObject *)(op))
+
 typedef struct {
     PyObject            *inobj;
     Py_ssize_t          inpos, inlen;
@@ -136,9 +157,10 @@ call_error_callback(PyObject *errors, PyObject *exc)
 }
 
 static PyObject *
-codecctx_errors_get(MultibyteStatefulCodecContext *self, void *Py_UNUSED(ignored))
+codecctx_errors_get(PyObject *op, void *Py_UNUSED(closure))
 {
     const char *errors;
+    MultibyteStatefulCodecContext *self = _MultibyteStatefulCodecContext_CAST(op);
 
     if (self->errors == ERROR_STRICT)
         errors = "strict";
@@ -154,11 +176,11 @@ codecctx_errors_get(MultibyteStatefulCodecContext *self, void *Py_UNUSED(ignored
 }
 
 static int
-codecctx_errors_set(MultibyteStatefulCodecContext *self, PyObject *value,
-                    void *closure)
+codecctx_errors_set(PyObject *op, PyObject *value, void *Py_UNUSED(closure))
 {
     PyObject *cb;
     const char *str;
+    MultibyteStatefulCodecContext *self = _MultibyteStatefulCodecContext_CAST(op);
 
     if (value == NULL) {
         PyErr_SetString(PyExc_AttributeError, "cannot delete attribute");
@@ -184,9 +206,8 @@ codecctx_errors_set(MultibyteStatefulCodecContext *self, PyObject *value,
 
 /* This getset handlers list is used by all the stateful codec objects */
 static PyGetSetDef codecctx_getsets[] = {
-    {"errors",          (getter)codecctx_errors_get,
-                    (setter)codecctx_errors_set,
-                    PyDoc_STR("how to treat errors")},
+    {"errors", codecctx_errors_get, codecctx_errors_set,
+     PyDoc_STR("how to treat errors")},
     {NULL,}
 };
 
@@ -719,22 +740,24 @@ static struct PyMethodDef multibytecodec_methods[] = {
 };
 
 static int
-multibytecodec_clear(MultibyteCodecObject *self)
+multibytecodec_clear(PyObject *op)
 {
+    MultibyteCodecObject *self = _MultibyteCodecObject_CAST(op);
     Py_CLEAR(self->cjk_module);
     return 0;
 }
 
 static int
-multibytecodec_traverse(MultibyteCodecObject *self, visitproc visit, void *arg)
+multibytecodec_traverse(PyObject *op, visitproc visit, void *arg)
 {
+    MultibyteCodecObject *self = _MultibyteCodecObject_CAST(op);
     Py_VISIT(Py_TYPE(self));
     Py_VISIT(self->cjk_module);
     return 0;
 }
 
 static void
-multibytecodec_dealloc(MultibyteCodecObject *self)
+multibytecodec_dealloc(PyObject *self)
 {
     PyObject_GC_UnTrack(self);
     PyTypeObject *tp = Py_TYPE(self);
@@ -1106,17 +1129,18 @@ mbiencoder_init(PyObject *self, PyObject *args, PyObject *kwds)
 }
 
 static int
-mbiencoder_traverse(MultibyteIncrementalEncoderObject *self,
-                    visitproc visit, void *arg)
+mbiencoder_traverse(PyObject *op, visitproc visit, void *arg)
 {
+    MultibyteIncrementalEncoderObject *self = _MultibyteIncrementalEncoderObject_CAST(op);
     if (ERROR_ISCUSTOM(self->errors))
         Py_VISIT(self->errors);
     return 0;
 }
 
 static void
-mbiencoder_dealloc(MultibyteIncrementalEncoderObject *self)
+mbiencoder_dealloc(PyObject *op)
 {
+    MultibyteIncrementalEncoderObject *self = _MultibyteIncrementalEncoderObject_CAST(op);
     PyTypeObject *tp = Py_TYPE(self);
     PyObject_GC_UnTrack(self);
     ERROR_DECREF(self->errors);
@@ -1388,17 +1412,18 @@ mbidecoder_init(PyObject *self, PyObject *args, PyObject *kwds)
 }
 
 static int
-mbidecoder_traverse(MultibyteIncrementalDecoderObject *self,
-                    visitproc visit, void *arg)
+mbidecoder_traverse(PyObject *op, visitproc visit, void *arg)
 {
+    MultibyteIncrementalDecoderObject *self = _MultibyteIncrementalDecoderObject_CAST(op);
     if (ERROR_ISCUSTOM(self->errors))
         Py_VISIT(self->errors);
     return 0;
 }
 
 static void
-mbidecoder_dealloc(MultibyteIncrementalDecoderObject *self)
+mbidecoder_dealloc(PyObject *op)
 {
+    MultibyteIncrementalDecoderObject *self = _MultibyteIncrementalDecoderObject_CAST(op);
     PyTypeObject *tp = Py_TYPE(self);
     PyObject_GC_UnTrack(self);
     ERROR_DECREF(self->errors);
@@ -1704,9 +1729,9 @@ mbstreamreader_init(PyObject *self, PyObject *args, PyObject *kwds)
 }
 
 static int
-mbstreamreader_traverse(MultibyteStreamReaderObject *self,
-                        visitproc visit, void *arg)
+mbstreamreader_traverse(PyObject *op, visitproc visit, void *arg)
 {
+    MultibyteStreamReaderObject *self = _MultibyteStreamReaderObject_CAST(op);
     if (ERROR_ISCUSTOM(self->errors))
         Py_VISIT(self->errors);
     Py_VISIT(self->stream);
@@ -1714,8 +1739,9 @@ mbstreamreader_traverse(MultibyteStreamReaderObject *self,
 }
 
 static void
-mbstreamreader_dealloc(MultibyteStreamReaderObject *self)
+mbstreamreader_dealloc(PyObject *op)
 {
+    MultibyteStreamReaderObject *self = _MultibyteStreamReaderObject_CAST(op);
     PyTypeObject *tp = Py_TYPE(self);
     PyObject_GC_UnTrack(self);
     ERROR_DECREF(self->errors);
@@ -1927,9 +1953,9 @@ mbstreamwriter_init(PyObject *self, PyObject *args, PyObject *kwds)
 }
 
 static int
-mbstreamwriter_traverse(MultibyteStreamWriterObject *self,
-                        visitproc visit, void *arg)
+mbstreamwriter_traverse(PyObject *op, visitproc visit, void *arg)
 {
+    MultibyteStreamWriterObject *self = _MultibyteStreamWriterObject_CAST(op);
     if (ERROR_ISCUSTOM(self->errors))
         Py_VISIT(self->errors);
     Py_VISIT(self->stream);
@@ -1937,8 +1963,9 @@ mbstreamwriter_traverse(MultibyteStreamWriterObject *self,
 }
 
 static void
-mbstreamwriter_dealloc(MultibyteStreamWriterObject *self)
+mbstreamwriter_dealloc(PyObject *op)
 {
+    MultibyteStreamWriterObject *self = _MultibyteStreamWriterObject_CAST(op);
     PyTypeObject *tp = Py_TYPE(self);
     PyObject_GC_UnTrack(self);
     ERROR_DECREF(self->errors);
@@ -2044,7 +2071,7 @@ _multibytecodec_clear(PyObject *mod)
 static void
 _multibytecodec_free(void *mod)
 {
-    _multibytecodec_clear((PyObject *)mod);
+    (void)_multibytecodec_clear((PyObject *)mod);
 }
 
 #define CREATE_TYPE(module, type, spec)                                      \