diff --git a/ChangeLog.d/fix_tls_alert_codes.txt b/ChangeLog.d/fix_tls_alert_codes.txt
new file mode 100644
index 0000000000..10235d7bc3
--- /dev/null
+++ b/ChangeLog.d/fix_tls_alert_codes.txt
@@ -0,0 +1,5 @@
+Bugfix
+   * Fix which alert is sent in some cases to conform to the
+     applicable RFC: on an invalid Finished message value, an
+     invalid max_fragment_length extension, or an
+     unsupported extension used by the server.
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 01e3f111e8..f49178cf41 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -1525,7 +1525,7 @@ static int ssl_parse_max_fragment_length_ext( mbedtls_ssl_context *ssl,
         mbedtls_ssl_send_alert_message(
             ssl,
             MBEDTLS_SSL_ALERT_LEVEL_FATAL,
-            MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
+            MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER );
         return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
     }
 
@@ -1572,7 +1572,7 @@ static int ssl_parse_cid_ext( mbedtls_ssl_context *ssl,
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "CID extension unexpected" ) );
         mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
-                                     MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
+                                     MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT );
         return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
     }
 
@@ -1628,7 +1628,7 @@ static int ssl_parse_encrypt_then_mac_ext( mbedtls_ssl_context *ssl,
         mbedtls_ssl_send_alert_message(
             ssl,
             MBEDTLS_SSL_ALERT_LEVEL_FATAL,
-            MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
+            MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT );
         return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
     }
 
@@ -1654,7 +1654,7 @@ static int ssl_parse_extended_ms_ext( mbedtls_ssl_context *ssl,
         mbedtls_ssl_send_alert_message(
             ssl,
             MBEDTLS_SSL_ALERT_LEVEL_FATAL,
-            MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
+            MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT );
         return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
     }
 
@@ -1679,7 +1679,7 @@ static int ssl_parse_session_ticket_ext( mbedtls_ssl_context *ssl,
         mbedtls_ssl_send_alert_message(
             ssl,
             MBEDTLS_SSL_ALERT_LEVEL_FATAL,
-            MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
+            MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT );
         return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
     }
 
@@ -1785,7 +1785,7 @@ static int ssl_parse_alpn_ext( mbedtls_ssl_context *ssl,
         mbedtls_ssl_send_alert_message(
             ssl,
             MBEDTLS_SSL_ALERT_LEVEL_FATAL,
-            MBEDTLS_SSL_ALERT_MSG_HANDSHAKE_FAILURE );
+            MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT );
         return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
     }
 
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index a4cf44c788..976a87c514 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -3610,7 +3610,7 @@ int mbedtls_ssl_parse_finished( mbedtls_ssl_context *ssl )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad finished message" ) );
         mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
-                                        MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
+                                        MBEDTLS_SSL_ALERT_MSG_DECRYPT_ERROR );
         return( MBEDTLS_ERR_SSL_BAD_HS_FINISHED );
     }
 
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 2200f9036d..5954004d47 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -5992,7 +5992,7 @@ run_test    "ECJPAKE: working, TLS" \
             -S "SSL - Verification of the message MAC failed"
 
 server_needs_more_time 1
-requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECJPAKE
+requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED
 run_test    "ECJPAKE: password mismatch, TLS" \
             "$P_SRV debug_level=3 ecjpake_pw=bla" \
             "$P_CLI debug_level=3 ecjpake_pw=bad \
@@ -6001,7 +6001,7 @@ run_test    "ECJPAKE: password mismatch, TLS" \
             -C "re-using cached ecjpake parameters" \
             -s "SSL - Verification of the message MAC failed"
 
-requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECJPAKE
+requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED
 run_test    "ECJPAKE: working, DTLS" \
             "$P_SRV debug_level=3 dtls=1 ecjpake_pw=bla" \
             "$P_CLI debug_level=3 dtls=1 ecjpake_pw=bla \
@@ -6010,7 +6010,7 @@ run_test    "ECJPAKE: working, DTLS" \
             -c "re-using cached ecjpake parameters" \
             -S "SSL - Verification of the message MAC failed"
 
-requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECJPAKE
+requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED
 run_test    "ECJPAKE: working, DTLS, no cookie" \
             "$P_SRV debug_level=3 dtls=1 ecjpake_pw=bla cookies=0" \
             "$P_CLI debug_level=3 dtls=1 ecjpake_pw=bla \
@@ -6020,7 +6020,7 @@ run_test    "ECJPAKE: working, DTLS, no cookie" \
             -S "SSL - Verification of the message MAC failed"
 
 server_needs_more_time 1
-requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECJPAKE
+requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED
 run_test    "ECJPAKE: password mismatch, DTLS" \
             "$P_SRV debug_level=3 dtls=1 ecjpake_pw=bla" \
             "$P_CLI debug_level=3 dtls=1 ecjpake_pw=bad \
@@ -6030,7 +6030,7 @@ run_test    "ECJPAKE: password mismatch, DTLS" \
             -s "SSL - Verification of the message MAC failed"
 
 # for tests with configs/config-thread.h
-requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECJPAKE
+requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED
 run_test    "ECJPAKE: working, DTLS, nolog" \
             "$P_SRV dtls=1 ecjpake_pw=bla" \
             "$P_CLI dtls=1 ecjpake_pw=bla \