error: invalid conversion on const return type

Using g++ version 4.8.4 I get an error:

error: invalid conversion from ‘const SSL_METHOD* ()() {aka const ssl_method_st ()()}’ to ‘MethodFuncPtr {aka ssl_method_st (*)()}’ [-fpermissive]

I can compile with -fpermissive, but what is a fix? I've seen solutions for this type of error, but none for when the return type is const (even though it's explicitly a const return value).

A snippet from ssl.h (C header):

#ifdef  __cplusplus
extern "C" {
#endif

  typedef struct ssl_method_st {
    int version;
    int (*ssl_new) (int *s);
    void (*ssl_clear) (int *s);
  } SSL_METHOD;

  const SSL_METHOD *TLSv1_method(void);

#ifdef  __cplusplus
}

endif

C++ header:

#include <ssl.h>

extern "C" {
  typedef SSL_METHOD*(*MethodFuncPtr)(void);
}

class Method
{
 public:
  Method(SSL_METHOD *method);

  static const MethodFuncPtr TLSv1;

 private:
  SSL_METHOD *m_method;
};

C++ source:

Method::Method(SSL_METHOD* method)
  : m_method(method)
{ }

const MethodFuncPtr Method::TLSv1 = TLSv1_method;