diff --git a/src/calibre/srv/fast_css_transform.cpp b/src/calibre/srv/fast_css_transform.cpp
index 53a1baaf14..bb4dbc171a 100644
--- a/src/calibre/srv/fast_css_transform.cpp
+++ b/src/calibre/srv/fast_css_transform.cpp
@@ -242,7 +242,7 @@ class Token {
             out.push_back('\\');
             if (is_whitespace(ch) || is_hex_digit(ch)) {
                 char buf[8];
-                int num = std::snprintf(buf, sizeof(buf), "%x ", ch);
+                int num = std::snprintf(buf, sizeof(buf), "%x ", (unsigned int)ch);
                 if (num > 0) {
                     out.resize(out.size() + num);
                     for (int i = 0; i < num; i++) out[i + out.size() - num] = buf[i];
diff --git a/src/calibre/utils/windows/winutil.cpp b/src/calibre/utils/windows/winutil.cpp
index a769e76846..6d48a537b2 100644
--- a/src/calibre/utils/windows/winutil.cpp
+++ b/src/calibre/utils/windows/winutil.cpp
@@ -61,7 +61,7 @@ PyGUID_dealloc(PyGUID *self) { }
 static PyObject*
 PyGUID_repr(PyGUID *self) {
 	com_wchar_raii s;
-	HRESULT hr = StringFromIID(self->guid, s.address());
+	HRESULT hr = StringFromIID(self->guid, s.unsafe_address());
 	if (FAILED(hr)) return error_from_hresult(hr);
 	return PyUnicode_FromWideChar(s.ptr(), -1);
 }
@@ -317,7 +317,7 @@ known_folder_path(PyObject *self, PyObject *args) {
 	DWORD flags = KF_FLAG_DEFAULT;
 	if (!PyArg_ParseTuple(args, "O!|k", &PyGUIDType, &id, &flags)) return NULL;
 	com_wchar_raii path;
-	HRESULT hr = SHGetKnownFolderPath(id->guid, flags, NULL, path.address());
+	HRESULT hr = SHGetKnownFolderPath(id->guid, flags, NULL, path.unsafe_address());
 	return PyUnicode_FromWideChar(path.ptr(), -1);
 }