error: field 'm_enc' has incomplete type

When I run make I get the following error:
```
In file included from /home/nishka/MPCHonestMajority/AES_PRG.cpp:3:
/home/nishka/MPCHonestMajority/AES_PRG.h:46:20: error: field ‘m_enc’ has incomplete type ‘EVP_CIPHER_CTX’ {aka ‘evp_cipher_ctx_st’}
   46 |     EVP_CIPHER_CTX m_enc;
      |                    ^~~~~

```
What can I do to fix it?