diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index ac0ffb00e785c3..cf298b0fb49182 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -2497,22 +2497,30 @@ PyCSimpleType_init(PyObject *self, PyObject *args, PyObject *kwds)
         }
         assert(sw_info);
 #ifdef WORDS_BIGENDIAN
-        PyObject_SetAttrString(self, "__ctype_le__", swapped);
-        PyObject_SetAttrString(self, "__ctype_be__", self);
-        PyObject_SetAttrString(swapped, "__ctype_be__", self);
-        PyObject_SetAttrString(swapped, "__ctype_le__", swapped);
+        if (PyObject_SetAttrString(self, "__ctype_le__", swapped) < 0 ||
+            PyObject_SetAttrString(self, "__ctype_be__", self) < 0 ||
+            PyObject_SetAttrString(swapped, "__ctype_be__", self) < 0 ||
+            PyObject_SetAttrString(swapped, "__ctype_le__", swapped) < 0)
+       {
+            Py_DECREF(swapped);
+            return -1;
+        }
         /* We are creating the type for the OTHER endian */
         sw_info->format = _ctypes_alloc_format_string("<", stginfo->format+1);
 #else
-        PyObject_SetAttrString(self, "__ctype_be__", swapped);
-        PyObject_SetAttrString(self, "__ctype_le__", self);
-        PyObject_SetAttrString(swapped, "__ctype_le__", self);
-        PyObject_SetAttrString(swapped, "__ctype_be__", swapped);
+        if (PyObject_SetAttrString(self, "__ctype_be__", swapped) < 0 ||
+            PyObject_SetAttrString(self, "__ctype_le__", self) < 0 ||
+            PyObject_SetAttrString(swapped, "__ctype_le__", self) < 0 ||
+            PyObject_SetAttrString(swapped, "__ctype_be__", swapped) < 0)
+        {
+            Py_DECREF(swapped);
+            return -1;
+        }
         /* We are creating the type for the OTHER endian */
         sw_info->format = _ctypes_alloc_format_string(">", stginfo->format+1);
 #endif
         Py_DECREF(swapped);
-        if (PyErr_Occurred()) {
+        if (sw_info->format == NULL) {
             return -1;
         }
     };
diff --git a/Modules/_interpchannelsmodule.c b/Modules/_interpchannelsmodule.c
index 351509d57de16e..6516d4592f5eef 100644
--- a/Modules/_interpchannelsmodule.c
+++ b/Modules/_interpchannelsmodule.c
@@ -2638,7 +2638,7 @@ _channelid_shared(PyThreadState *tstate, PyObject *obj, _PyXIData_t *data)
     if (st == NULL) {
         return -1;
     }
-    if (!PyObject_IsInstance(obj, (PyObject *)st->ChannelIDType)) {
+    if (!PyObject_TypeCheck(obj, st->ChannelIDType)) {
         PyErr_Format(PyExc_TypeError,
                      "'_id' attribute must be an %N object, not %T",
                      st->ChannelIDType, obj);
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index fe55ec7cafffec..83d5f43f8991e3 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -2835,8 +2835,14 @@ init_sys_streams(PyThreadState *tstate)
                        config->stdio_errors);
     if (std == NULL)
         goto error;
-    PySys_SetObject("__stdin__", std);
-    _PySys_SetAttr(&_Py_ID(stdin), std);
+    if (PySys_SetObject("__stdin__", std) < 0) {
+        Py_DECREF(std);
+        goto error;
+    }
+    if (_PySys_SetAttr(&_Py_ID(stdin), std) < 0) {
+        Py_DECREF(std);
+        goto error;
+    }
     Py_DECREF(std);
 
     /* Set sys.stdout */
@@ -2846,8 +2852,14 @@ init_sys_streams(PyThreadState *tstate)
                        config->stdio_errors);
     if (std == NULL)
         goto error;
-    PySys_SetObject("__stdout__", std);
-    _PySys_SetAttr(&_Py_ID(stdout), std);
+    if (PySys_SetObject("__stdout__", std) < 0) {
+        Py_DECREF(std);
+        goto error;
+    }
+    if (_PySys_SetAttr(&_Py_ID(stdout), std) < 0) {
+        Py_DECREF(std);
+        goto error;
+    }
     Py_DECREF(std);
 
 #if 1 /* Disable this if you have trouble debugging bootstrap stuff */