diff --git a/crypto-openssl.cpp b/crypto-openssl.cpp
index 48d7af5..cb168fc 100644
--- a/crypto-openssl.cpp
+++ b/crypto-openssl.cpp
@@ -43,7 +43,7 @@ void init_crypto ()
 	ERR_load_crypto_strings();
 }
 
-struct Aes_impl {
+struct Aes_ecb_encryptor::Aes_impl {
 	AES_KEY key;
 };
 
@@ -66,7 +66,7 @@ void Aes_ecb_encryptor::encrypt(const unsigned char* plain, unsigned char* ciphe
 	AES_encrypt(plain, cipher, &(impl->key));
 }
 
-struct Hmac_impl {
+struct Hmac_sha1_state::Hmac_impl {
 	HMAC_CTX ctx;
 };
 
diff --git a/crypto.hpp b/crypto.hpp
index 4eedc07..adc9643 100644
--- a/crypto.hpp
+++ b/crypto.hpp
@@ -47,8 +47,6 @@ struct Crypto_error {
 	Crypto_error (const std::string& w, const std::string& m) : where(w), message(m) { }
 };
 
-struct Aes_impl;
-
 class Aes_ecb_encryptor {
 public:
 	enum {
@@ -57,6 +55,8 @@ public:
 	};
 
 private:
+	struct Aes_impl;
+
 	std::auto_ptr<Aes_impl>	impl;
 
 public:
@@ -91,8 +91,6 @@ public:
 
 typedef Aes_ctr_encryptor Aes_ctr_decryptor;
 
-struct Hmac_impl;
-
 class Hmac_sha1_state {
 public:
 	enum {
@@ -101,6 +99,8 @@ public:
 	};
 
 private:
+	struct Hmac_impl;
+
 	std::auto_ptr<Hmac_impl>	impl;
 
 public: