diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index 85c1de8..3e48cf9 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -1023,6 +1023,10 @@
 #error "MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH defined, but not all prerequisites"
 #endif
 
+#if defined(MBEDTLS_SSL_RECORD_SIZE_LIMIT) && ( !defined(MBEDTLS_SSL_PROTO_TLS1_3) )
+#error "MBEDTLS_SSL_RECORD_SIZE_LIMIT defined, but not all prerequisites"
+#endif
+
 #if defined(MBEDTLS_SSL_CONTEXT_SERIALIZATION) && !( defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CCM_C) || defined(MBEDTLS_CHACHAPOLY_C) )
 #error "MBEDTLS_SSL_CONTEXT_SERIALIZATION defined, but not all prerequisites"
 #endif
diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h
index 1ea241c..42485b7 100644
--- a/include/mbedtls/mbedtls_config.h
+++ b/include/mbedtls/mbedtls_config.h
@@ -1548,6 +1548,20 @@
 #define MBEDTLS_SSL_MAX_FRAGMENT_LENGTH
 
 /**
+ * \def MBEDTLS_SSL_RECORD_SIZE_LIMIT
+ *
+ * Enable support for RFC 8449 record_size_limit extension in SSL (TLS 1.3 only).
+ *
+ * \warning This extension is currently in development and must NOT be used except
+ *          for testing purposes.
+ *
+ * Requires: MBEDTLS_SSL_PROTO_TLS1_3
+ *
+ * Uncomment this macro to enable support for the record_size_limit extension
+ */
+//#define MBEDTLS_SSL_RECORD_SIZE_LIMIT
+
+/**
  * \def MBEDTLS_SSL_PROTO_TLS1_2
  *
  * Enable support for TLS 1.2 (and DTLS 1.2 if DTLS is enabled).
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 29ba85a..efe0830 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -571,6 +571,8 @@
 #define MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC            22 /* 0x16 */
 #define MBEDTLS_TLS_EXT_EXTENDED_MASTER_SECRET  0x0017 /* 23 */
 
+#define MBEDTLS_TLS_EXT_RECORD_SIZE_LIMIT           28 /* RFC 8449 (implemented for TLS 1.3 only) */
+
 #define MBEDTLS_TLS_EXT_SESSION_TICKET              35
 
 #define MBEDTLS_TLS_EXT_PRE_SHARED_KEY              41 /* RFC 8446 TLS 1.3 */
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 4cdd87e..6fe0414 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -107,6 +107,7 @@
 #define MBEDTLS_SSL_EXT_ID_ENCRYPT_THEN_MAC           25
 #define MBEDTLS_SSL_EXT_ID_EXTENDED_MASTER_SECRET     26
 #define MBEDTLS_SSL_EXT_ID_SESSION_TICKET             27
+#define MBEDTLS_SSL_EXT_ID_RECORD_SIZE_LIMIT          28
 
 /* Utility for translating IANA extension type. */
 uint32_t mbedtls_ssl_get_extension_id(unsigned int extension_type);
@@ -167,6 +168,7 @@
      MBEDTLS_SSL_EXT_MASK(CERT_AUTH)                              | \
      MBEDTLS_SSL_EXT_MASK(POST_HANDSHAKE_AUTH)                    | \
      MBEDTLS_SSL_EXT_MASK(SIG_ALG_CERT)                           | \
+     MBEDTLS_SSL_EXT_MASK(RECORD_SIZE_LIMIT)                      | \
      MBEDTLS_SSL_TLS1_3_EXT_MASK_UNRECOGNIZED)
 
 /* RFC 8446 section 4.2. Allowed extensions for EncryptedExtensions */
@@ -179,7 +181,8 @@
      MBEDTLS_SSL_EXT_MASK(ALPN)                                   | \
      MBEDTLS_SSL_EXT_MASK(CLI_CERT_TYPE)                          | \
      MBEDTLS_SSL_EXT_MASK(SERV_CERT_TYPE)                         | \
-     MBEDTLS_SSL_EXT_MASK(EARLY_DATA))
+     MBEDTLS_SSL_EXT_MASK(EARLY_DATA)                             | \
+     MBEDTLS_SSL_EXT_MASK(RECORD_SIZE_LIMIT))
 
 /* RFC 8446 section 4.2. Allowed extensions for CertificateRequest */
 #define MBEDTLS_SSL_TLS1_3_ALLOWED_EXTS_OF_CR                                  \
@@ -2662,6 +2665,16 @@
                                       const unsigned char *end);
 #endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
 
+#if defined(MBEDTLS_SSL_RECORD_SIZE_LIMIT)
+#define MBEDTLS_SSL_RECORD_SIZE_LIMIT_EXTENSION_DATA_LENGTH (2)
+#define MBEDTLS_SSL_RECORD_SIZE_LIMIT_MIN (64)
+
+MBEDTLS_CHECK_RETURN_CRITICAL
+int mbedtls_ssl_tls13_parse_record_size_limit_ext(mbedtls_ssl_context *ssl,
+                                                  const unsigned char *buf,
+                                                  const unsigned char *end);
+#endif /* MBEDTLS_SSL_RECORD_SIZE_LIMIT */
+
 #if defined(MBEDTLS_SSL_ALPN)
 MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_parse_alpn_ext(mbedtls_ssl_context *ssl,
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index b17da06..a6129da 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -591,6 +591,9 @@
         case MBEDTLS_TLS_EXT_EXTENDED_MASTER_SECRET:
             return MBEDTLS_SSL_EXT_ID_EXTENDED_MASTER_SECRET;
 
+        case MBEDTLS_TLS_EXT_RECORD_SIZE_LIMIT:
+            return MBEDTLS_SSL_EXT_ID_RECORD_SIZE_LIMIT;
+
         case MBEDTLS_TLS_EXT_SESSION_TICKET:
             return MBEDTLS_SSL_EXT_ID_SESSION_TICKET;
 
@@ -633,7 +636,8 @@
     [MBEDTLS_SSL_EXT_ID_SUPPORTED_POINT_FORMATS] = "supported_point_formats",
     [MBEDTLS_SSL_EXT_ID_ENCRYPT_THEN_MAC] = "encrypt_then_mac",
     [MBEDTLS_SSL_EXT_ID_EXTENDED_MASTER_SECRET] = "extended_master_secret",
-    [MBEDTLS_SSL_EXT_ID_SESSION_TICKET] = "session_ticket"
+    [MBEDTLS_SSL_EXT_ID_SESSION_TICKET] = "session_ticket",
+    [MBEDTLS_SSL_EXT_ID_RECORD_SIZE_LIMIT] = "record_size_limit"
 };
 
 static unsigned int extension_type_table[] = {
@@ -664,7 +668,8 @@
     [MBEDTLS_SSL_EXT_ID_SUPPORTED_POINT_FORMATS] = MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS,
     [MBEDTLS_SSL_EXT_ID_ENCRYPT_THEN_MAC] = MBEDTLS_TLS_EXT_ENCRYPT_THEN_MAC,
     [MBEDTLS_SSL_EXT_ID_EXTENDED_MASTER_SECRET] = MBEDTLS_TLS_EXT_EXTENDED_MASTER_SECRET,
-    [MBEDTLS_SSL_EXT_ID_SESSION_TICKET] = MBEDTLS_TLS_EXT_SESSION_TICKET
+    [MBEDTLS_SSL_EXT_ID_SESSION_TICKET] = MBEDTLS_TLS_EXT_SESSION_TICKET,
+    [MBEDTLS_SSL_EXT_ID_RECORD_SIZE_LIMIT] = MBEDTLS_TLS_EXT_RECORD_SIZE_LIMIT
 };
 
 const char *mbedtls_ssl_get_extension_name(unsigned int extension_type)
diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index a72f770..a7feced 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -2117,10 +2117,11 @@
     extensions_len = MBEDTLS_GET_UINT16_BE(p, 0);
     p += 2;
 
-    MBEDTLS_SSL_DEBUG_BUF(3, "encrypted extensions", p, extensions_len);
     MBEDTLS_SSL_CHK_BUF_READ_PTR(p, end, extensions_len);
     extensions_end = p + extensions_len;
 
+    MBEDTLS_SSL_DEBUG_BUF(3, "encrypted extensions", p, extensions_len);
+
     handshake->received_extensions = MBEDTLS_SSL_EXT_MASK_NONE;
 
     while (p < extensions_end) {
@@ -2172,6 +2173,19 @@
                 break;
 #endif /* MBEDTLS_SSL_EARLY_DATA */
 
+#if defined(MBEDTLS_SSL_RECORD_SIZE_LIMIT)
+            case MBEDTLS_TLS_EXT_RECORD_SIZE_LIMIT:
+                MBEDTLS_SSL_DEBUG_MSG(3, ("found record_size_limit extension"));
+
+                ret = mbedtls_ssl_tls13_parse_record_size_limit_ext(ssl, p, p + extension_data_len);
+
+                /* TODO: Return unconditionally here until we handle the record size limit correctly.
+                 *            Once handled correctly, only return in case of errors. */
+                return ret;
+
+                break;
+#endif /* MBEDTLS_SSL_RECORD_SIZE_LIMIT */
+
             default:
                 MBEDTLS_SSL_PRINT_EXT(
                     3, MBEDTLS_SSL_HS_ENCRYPTED_EXTENSIONS,
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 512656e..669a90a 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -1567,4 +1567,61 @@
     return MBEDTLS_ERR_SSL_UNSUPPORTED_EXTENSION;
 }
 
+#if defined(MBEDTLS_SSL_RECORD_SIZE_LIMIT)
+/* RFC 8449, section 4:
+ *
+ * The ExtensionData of the "record_size_limit" extension is
+ * RecordSizeLimit:
+ *     uint16 RecordSizeLimit;
+ */
+MBEDTLS_CHECK_RETURN_CRITICAL
+int mbedtls_ssl_tls13_parse_record_size_limit_ext(mbedtls_ssl_context *ssl,
+                                                  const unsigned char *buf,
+                                                  const unsigned char *end)
+{
+    const unsigned char *p = buf;
+    uint16_t record_size_limit;
+    const size_t extension_data_len = end - buf;
+
+    if (extension_data_len != MBEDTLS_SSL_RECORD_SIZE_LIMIT_EXTENSION_DATA_LENGTH) {
+        MBEDTLS_SSL_DEBUG_MSG(2,
+                              ("record_size_limit extension has invalid length: %"
+                               MBEDTLS_PRINTF_SIZET " Bytes",
+                               extension_data_len));
+
+        MBEDTLS_SSL_PEND_FATAL_ALERT(
+            MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER,
+            MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER);
+        return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
+    }
+
+    MBEDTLS_SSL_CHK_BUF_READ_PTR(p, end, 2);
+    record_size_limit = MBEDTLS_GET_UINT16_BE(p, 0);
+
+    MBEDTLS_SSL_DEBUG_MSG(2, ("RecordSizeLimit: %u Bytes", record_size_limit));
+
+    /* RFC 8449, section 4
+     *
+     * Endpoints MUST NOT send a "record_size_limit" extension with a value
+     * smaller than 64.  An endpoint MUST treat receipt of a smaller value
+     * as a fatal error and generate an "illegal_parameter" alert.
+     */
+    if (record_size_limit < MBEDTLS_SSL_RECORD_SIZE_LIMIT_MIN) {
+        MBEDTLS_SSL_PEND_FATAL_ALERT(
+            MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER,
+            MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER);
+        return MBEDTLS_ERR_SSL_ILLEGAL_PARAMETER;
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG(2,
+                          (
+                              "record_size_limit extension is still in development. Aborting handshake."));
+
+    MBEDTLS_SSL_PEND_FATAL_ALERT(
+        MBEDTLS_SSL_ALERT_MSG_UNSUPPORTED_EXT,
+        MBEDTLS_ERR_SSL_UNSUPPORTED_EXTENSION);
+    return MBEDTLS_ERR_SSL_UNSUPPORTED_EXTENSION;
+}
+#endif /* MBEDTLS_SSL_RECORD_SIZE_LIMIT */
+
 #endif /* MBEDTLS_SSL_TLS_C && MBEDTLS_SSL_PROTO_TLS1_3 */
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index 6b1c4c5..bccf9ab 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -1585,6 +1585,19 @@
                 break;
 #endif /* MBEDTLS_SSL_TLS1_3_KEY_EXCHANGE_MODE_EPHEMERAL_ENABLED */
 
+#if defined(MBEDTLS_SSL_RECORD_SIZE_LIMIT)
+            case MBEDTLS_TLS_EXT_RECORD_SIZE_LIMIT:
+                MBEDTLS_SSL_DEBUG_MSG(3, ("found record_size_limit extension"));
+
+                ret = mbedtls_ssl_tls13_parse_record_size_limit_ext(ssl, p, extension_data_end);
+
+                /* TODO: Return unconditionally here until we handle the record size limit correctly.
+                 *            Once handled correctly, only return in case of errors. */
+                return ret;
+
+                break;
+#endif /* MBEDTLS_SSL_RECORD_SIZE_LIMIT */
+
             default:
                 MBEDTLS_SSL_PRINT_EXT(
                     3, MBEDTLS_SSL_HS_CLIENT_HELLO,
diff --git a/scripts/config.py b/scripts/config.py
index a53c470..404a5ef 100755
--- a/scripts/config.py
+++ b/scripts/config.py
@@ -215,6 +215,7 @@
     'MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN', # build dependency (clang+memsan)
     'MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND', # build dependency (valgrind headers)
     'MBEDTLS_X509_REMOVE_INFO', # removes a feature
+    'MBEDTLS_SSL_RECORD_SIZE_LIMIT', # in development, currently breaks other tests
 ])
 
 def is_seamless_alt(name):
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 5969e38..57395a6 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -3943,6 +3943,21 @@
     tests/ssl-opt.sh
 }
 
+component_test_tls13_only_record_size_limit () {
+    msg "build: TLS 1.3 only from default, record size limit extension enabled"
+    scripts/config.py set MBEDTLS_SSL_RECORD_SIZE_LIMIT
+    make CFLAGS="'-DMBEDTLS_USER_CONFIG_FILE=\"../tests/configs/tls13-only.h\"'"
+
+    msg "test_suite_ssl: TLS 1.3 only, record size limit extension enabled"
+    cd tests; ./test_suite_ssl; cd ..
+
+    msg "ssl-opt.sh: (TLS 1.3 only, record size limit extension tests only)"
+    # Both the server and the client will currently abort the handshake when they encounter the
+    # record size limit extension. There is no way to prevent gnutls-cli from sending the extension
+    # which makes all G_NEXT_CLI + P_SRV tests fail. Thus, run only the tests for the this extension.
+    tests/ssl-opt.sh -f "Record Size Limit"
+}
+
 component_build_mingw () {
     msg "build: Windows cross build - mingw64, make (Link Library)" # ~ 30s
     make CC=i686-w64-mingw32-gcc AR=i686-w64-mingw32-ar LD=i686-w64-minggw32-ld CFLAGS='-Werror -Wall -Wextra' WINDOWS_BUILD=1 lib programs
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 663f194..bae9ee5 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -4748,32 +4748,37 @@
 
 # Tests for Record Size Limit extension
 
-# gnutls feature tests: check if the record size limit extension is supported with TLS 1.2.
-requires_gnutls_record_size_limit
-run_test    "Record Size Limit: Test gnutls record size limit feature" \
-            "$G_NEXT_SRV --priority=NORMAL:-VERS-ALL:+VERS-TLS1.2:+CIPHER-ALL --disable-client-cert -d 4" \
-            "$G_NEXT_CLI localhost --priority=NORMAL:-VERS-ALL:+VERS-TLS1.2 -V -d 4" \
-            0 \
-            -c "Preparing extension (Record Size Limit/28) for 'client hello'"\
-            -s "Parsing extension 'Record Size Limit/28' (2 bytes)" \
-            -s "Preparing extension (Record Size Limit/28) for 'TLS 1.2 server hello'" \
-            -c "Parsing extension 'Record Size Limit/28' (2 bytes)" \
-            -s "Version: TLS1.2" \
-            -c "Version: TLS1.2"
-
-# gnutls feature tests: check if the record size limit extension is supported with TLS 1.3.
 requires_gnutls_tls1_3
 requires_gnutls_record_size_limit
-run_test    "Record Size Limit: TLS 1.3: Test gnutls record size limit feature" \
-            "$G_NEXT_SRV --priority=NORMAL:-VERS-ALL:+VERS-TLS1.3:+CIPHER-ALL --disable-client-cert -d 4" \
+requires_config_enabled MBEDTLS_SSL_RECORD_SIZE_LIMIT
+run_test    "Record Size Limit: TLS 1.3: Server-side parsing, debug output and fatal alert" \
+            "$P_SRV debug_level=3 force_version=tls13" \
             "$G_NEXT_CLI localhost --priority=NORMAL:-VERS-ALL:+VERS-TLS1.3 -V -d 4" \
+            1 \
+            -c "Preparing extension (Record Size Limit/28) for 'client hello'" \
+            -c "Sending extension Record Size Limit/28 (2 bytes)" \
+            -s "ClientHello: record_size_limit(28) extension received."\
+            -s "found record_size_limit extension" \
+            -s "RecordSizeLimit: 16385 Bytes" \
+            -c "Received alert \[110]: An unsupported extension was sent"
+
+requires_gnutls_tls1_3
+requires_gnutls_record_size_limit
+requires_gnutls_next_disable_tls13_compat
+requires_config_enabled MBEDTLS_SSL_RECORD_SIZE_LIMIT
+run_test    "Record Size Limit: TLS 1.3: Client-side parsing, debug output and fatal alert" \
+            "$G_NEXT_SRV --priority=NORMAL:-VERS-ALL:+VERS-TLS1.3:+CIPHER-ALL:%DISABLE_TLS13_COMPAT_MODE --disable-client-cert -d 4" \
+            "$P_CLI debug_level=4 force_version=tls13" \
             0 \
-            -c "Preparing extension (Record Size Limit/28) for 'client hello'"\
-            -s "Parsing extension 'Record Size Limit/28' (2 bytes)" \
-            -s "Preparing extension (Record Size Limit/28) for 'encrypted extensions'" \
-            -c "Parsing extension 'Record Size Limit/28' (2 bytes)" \
-            -s "Version: TLS1.3" \
-            -c "Version: TLS1.3"
+            -s "Preparing extension (Record Size Limit/28) for 'encrypted extensions'"
+# The P_CLI can not yet send the Record Size Limit extension. Thus, the G_NEXT_SRV does not send
+# a response in its EncryptedExtensions record.
+#            -s "Parsing extension 'Record Size Limit/28 (2 bytes)" \
+#            -s "Sending extension Record Size Limit/28 (2 bytes)" \
+#            -c "EncryptedExtensions: record_size_limit(28) extension received."\
+#            -c "found record_size_limit extension" \
+#            -c "RecordSizeLimit: 16385 Bytes" \
+#            -s "Received alert \[110]: An unsupported extension was sent"
 
 # Tests for renegotiation