Does this fix it?

Author: Skylion007

include/pybind11/pybind11.h

@@ -1947,6 +1947,23 @@ auto method_adaptor(Return (Class::*pmf)(Args...) const) -> Return (Derived::*)(
     return pmf;
 }
 
+template <typename Derived, typename Return, typename Class, typename... Args>
+auto method_adaptor(Return (Class::*pmf)(Args...) &) -> Return (Derived::*)(Args...) & {
+    static_assert(
+        detail::is_accessible_base_of<Class, Derived>::value,
+        "Cannot bind an inaccessible base class method; use a lambda definition instead");
+    return pmf;
+}
+
+template <typename Derived, typename Return, typename Class, typename... Args>
+auto method_adaptor(Return (Class::*pmf)(Args...) const &)
+    -> Return (Derived::*)(Args...) const & {
+    static_assert(
+        detail::is_accessible_base_of<Class, Derived>::value,
+        "Cannot bind an inaccessible base class method; use a lambda definition instead");
+    return pmf;
+}
+
 #ifdef __cpp_noexcept_function_type
 template <typename Derived, typename Return, typename Class, typename... Args>
 auto method_adaptor(Return (Class::*pmf)(Args...) noexcept)