diff --git a/cryptography/hazmat/backends/openssl/objects.py b/cryptography/hazmat/backends/openssl/objects.py
index ad1b858..0abc42d 100644
--- a/cryptography/hazmat/backends/openssl/objects.py
+++ b/cryptography/hazmat/backends/openssl/objects.py
@@ -31,7 +31,7 @@
 int OBJ_cmp(const ASN1_OBJECT *, const ASN1_OBJECT *);
 ASN1_OBJECT *OBJ_dup(const ASN1_OBJECT *);
 int OBJ_create(const char *, const char *, const char *);
-void OBJ_cleanup();
+void OBJ_cleanup(void);
 """
 
 MACROS = """
diff --git a/cryptography/hazmat/backends/openssl/ssl.py b/cryptography/hazmat/backends/openssl/ssl.py
index 49b142c..fb3b17e 100644
--- a/cryptography/hazmat/backends/openssl/ssl.py
+++ b/cryptography/hazmat/backends/openssl/ssl.py
@@ -255,9 +255,9 @@
 CUSTOMIZATIONS = """
 #ifdef OPENSSL_NO_SSL2
 static const long Cryptography_HAS_SSL2 = 0;
-SSL_METHOD* (*SSLv2_method)() = NULL;
-SSL_METHOD* (*SSLv2_client_method)() = NULL;
-SSL_METHOD* (*SSLv2_server_method)() = NULL;
+SSL_METHOD* (*SSLv2_method)(void) = NULL;
+SSL_METHOD* (*SSLv2_client_method)(void) = NULL;
+SSL_METHOD* (*SSLv2_server_method)(void) = NULL;
 #else
 static const long Cryptography_HAS_SSL2 = 1;
 #endif