diff --git a/ssl/CMakeLists.txt b/ssl/CMakeLists.txt
index 5d76fdf..b6f4451 100644
--- a/ssl/CMakeLists.txt
+++ b/ssl/CMakeLists.txt
@@ -35,9 +35,9 @@
   tls_method.cc
   tls_record.cc
   tls13_both.cc
-  tls13_client.c
+  tls13_client.cc
   tls13_enc.cc
-  tls13_server.c
+  tls13_server.cc
 )
 
 target_link_libraries(ssl crypto)
diff --git a/ssl/tls13_client.c b/ssl/tls13_client.cc
similarity index 97%
rename from ssl/tls13_client.c
rename to ssl/tls13_client.cc
index c92b539..7f961bf 100644
--- a/ssl/tls13_client.c
+++ b/ssl/tls13_client.cc
@@ -382,8 +382,8 @@
 
   /* Store the negotiated ALPN in the session. */
   if (ssl->s3->alpn_selected != NULL) {
-    hs->new_session->early_alpn =
-        BUF_memdup(ssl->s3->alpn_selected, ssl->s3->alpn_selected_len);
+    hs->new_session->early_alpn = (uint8_t *)BUF_memdup(
+        ssl->s3->alpn_selected, ssl->s3->alpn_selected_len);
     if (hs->new_session->early_alpn == NULL) {
       ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
       return ssl_hs_error;
@@ -645,7 +645,8 @@
 enum ssl_hs_wait_t tls13_client_handshake(SSL_HANDSHAKE *hs) {
   while (hs->tls13_state != state_done) {
     enum ssl_hs_wait_t ret = ssl_hs_error;
-    enum client_hs_state_t state = hs->tls13_state;
+    enum client_hs_state_t state =
+        static_cast<enum client_hs_state_t>(hs->tls13_state);
     switch (state) {
       case state_process_hello_retry_request:
         ret = do_process_hello_retry_request(hs);
@@ -703,14 +704,13 @@
 }
 
 int tls13_process_new_session_ticket(SSL *ssl) {
-  int ret = 0;
-  SSL_SESSION *session = SSL_SESSION_dup(ssl->s3->established_session,
-                                         SSL_SESSION_INCLUDE_NONAUTH);
-  if (session == NULL) {
+  bssl::UniquePtr<SSL_SESSION> session(SSL_SESSION_dup(
+      ssl->s3->established_session, SSL_SESSION_INCLUDE_NONAUTH));
+  if (!session) {
     return 0;
   }
 
-  ssl_session_rebase_time(ssl, session);
+  ssl_session_rebase_time(ssl, session.get());
 
   uint32_t server_timeout;
   CBS cbs, ticket, extensions;
@@ -723,7 +723,7 @@
       CBS_len(&cbs) != 0) {
     ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
     OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
-    goto err;
+    return 0;
   }
 
   /* Cap the renewable lifetime by the server advertised value. This avoids
@@ -745,7 +745,7 @@
                             OPENSSL_ARRAY_SIZE(ext_types),
                             1 /* ignore unknown */)) {
     ssl3_send_alert(ssl, SSL3_AL_FATAL, alert);
-    goto err;
+    return 0;
   }
 
   if (have_early_data_info && ssl->cert->enable_early_data) {
@@ -753,7 +753,7 @@
         CBS_len(&early_data_info) != 0) {
       ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_DECODE_ERROR);
       OPENSSL_PUT_ERROR(SSL, SSL_R_DECODE_ERROR);
-      goto err;
+      return 0;
     }
   }
 
@@ -761,16 +761,12 @@
   session->not_resumable = 0;
 
   if (ssl->ctx->new_session_cb != NULL &&
-      ssl->ctx->new_session_cb(ssl, session)) {
+      ssl->ctx->new_session_cb(ssl, session.get())) {
     /* |new_session_cb|'s return value signals that it took ownership. */
-    session = NULL;
+    session.release();
   }
 
-  ret = 1;
-
-err:
-  SSL_SESSION_free(session);
-  return ret;
+  return 1;
 }
 
 void ssl_clear_tls13_state(SSL_HANDSHAKE *hs) {
diff --git a/ssl/tls13_server.c b/ssl/tls13_server.cc
similarity index 97%
rename from ssl/tls13_server.c
rename to ssl/tls13_server.cc
index 25a7c2c..4e66016 100644
--- a/ssl/tls13_server.c
+++ b/ssl/tls13_server.cc
@@ -12,6 +12,13 @@
  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
 
+/* Per C99, various stdint.h macros are unavailable in C++ unless some macros
+ * are defined. C++11 overruled this decision, but older Android NDKs still
+ * require it. */
+#if !defined(__STDC_LIMIT_MACROS)
+#define __STDC_LIMIT_MACROS
+#endif
+
 #include <openssl/ssl.h>
 
 #include <assert.h>
@@ -417,8 +424,8 @@
 
   /* Store the initial negotiated ALPN in the session. */
   if (ssl->s3->alpn_selected != NULL) {
-    hs->new_session->early_alpn =
-        BUF_memdup(ssl->s3->alpn_selected, ssl->s3->alpn_selected_len);
+    hs->new_session->early_alpn = (uint8_t *)BUF_memdup(
+        ssl->s3->alpn_selected, ssl->s3->alpn_selected_len);
     if (hs->new_session->early_alpn == NULL) {
       ssl3_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_INTERNAL_ERROR);
       return ssl_hs_error;
@@ -670,7 +677,8 @@
      *
      * TODO(davidben): This will need to be updated for DTLS 1.3. */
     assert(!SSL_is_dtls(hs->ssl));
-    uint8_t header[4] = {SSL3_MT_FINISHED, 0, 0, hs->hash_len};
+    assert(hs->hash_len <= 0xff);
+    uint8_t header[4] = {SSL3_MT_FINISHED, 0, 0, static_cast<uint8_t>(hs->hash_len)};
     if (!SSL_TRANSCRIPT_update(&hs->transcript, header, sizeof(header)) ||
         !SSL_TRANSCRIPT_update(&hs->transcript, hs->expected_client_finished,
                                hs->hash_len) ||
@@ -832,7 +840,8 @@
 enum ssl_hs_wait_t tls13_server_handshake(SSL_HANDSHAKE *hs) {
   while (hs->tls13_state != state_done) {
     enum ssl_hs_wait_t ret = ssl_hs_error;
-    enum server_hs_state_t state = hs->tls13_state;
+    enum server_hs_state_t state =
+        static_cast<enum server_hs_state_t>(hs->tls13_state);
     switch (state) {
       case state_select_parameters:
         ret = do_select_parameters(hs);