diff --git a/ChangeLog.d/tls-hs-defrag-in.txt b/ChangeLog.d/tls-hs-defrag-in.txt
new file mode 100644
index 0000000..6bab02a
--- /dev/null
+++ b/ChangeLog.d/tls-hs-defrag-in.txt
@@ -0,0 +1,7 @@
+Bugfix
+   * Support re-assembly of fragmented handshake messages in TLS (both
+     1.2 and 1.3). The lack of support was causing handshake failures with
+     some servers, especially with TLS 1.3 in practice. There are a few
+     limitations, notably a fragmented ClientHello is only supported when
+     TLS 1.3 support is enabled. See the documentation of
+     mbedtls_ssl_handshake() for details.
diff --git a/framework b/framework
index b5dc86c..cab0c5f 160000
--- a/framework
+++ b/framework
@@ -1 +1 @@
-Subproject commit b5dc86cfe7f1f15626bc43e6720447a0a51860b9
+Subproject commit cab0c5fe19d5747cb9603552b80ebe64b9c67fdd
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 42fffbf..97b0dcb 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1724,7 +1724,16 @@
     int MBEDTLS_PRIVATE(early_data_state);
 #endif
 
-    unsigned MBEDTLS_PRIVATE(badmac_seen);       /*!< records with a bad MAC received    */
+    /** Multipurpose field.
+     *
+     * - DTLS: records with a bad MAC received.
+     * - TLS: accumulated length of handshake fragments (up to \c in_hslen).
+     *
+     * This field is multipurpose in order to preserve the ABI in the
+     * Mbed TLS 3.6 LTS branch. Until 3.6.2, it was only used in DTLS
+     * and called `badmac_seen`.
+     */
+    unsigned MBEDTLS_PRIVATE(badmac_seen_or_in_hsfraglen);
 
 #if defined(MBEDTLS_X509_CRT_PARSE_C)
     /** Callback to customize X.509 certificate chain verification          */
@@ -4440,6 +4449,10 @@
  *                 with \c mbedtls_ssl_read()), not handshake messages.
  *                 With DTLS, this affects both ApplicationData and handshake.
  *
+ * \note           Defragmentation of TLS handshake messages is supported
+ *                 with some limitations. See the documentation of
+ *                 mbedtls_ssl_handshake() for details.
+ *
  * \note           This sets the maximum length for a record's payload,
  *                 excluding record overhead that will be added to it, see
  *                 \c mbedtls_ssl_get_record_expansion().
@@ -4970,6 +4983,24 @@
  *                 if a negotiation involving TLS 1.3 takes place (this may
  *                 be the case even if TLS 1.3 is offered but eventually
  *                 not selected).
+ *
+ * \note           In TLS, reception of fragmented handshake messages is
+ *                 supported with some limitations (those limitations do
+ *                 not apply to DTLS, where defragmentation is fully
+ *                 supported):
+ *                 - On an Mbed TLS server that only accepts TLS 1.2,
+ *                   the initial ClientHello message must not be fragmented.
+ *                   A TLS 1.2 ClientHello may be fragmented if the server
+ *                   also accepts TLS 1.3 connections (meaning
+ *                   that #MBEDTLS_SSL_PROTO_TLS1_3 enabled, and the
+ *                   accepted versions have not been restricted with
+ *                   mbedtls_ssl_conf_max_tls_version() or the like).
+ *                 - The first fragment of a handshake message must be
+ *                   at least 4 bytes long.
+ *                 - Non-handshake records must not be interleaved between
+ *                   the fragments of a handshake message. (This is permitted
+ *                   in TLS 1.2 but not in TLS 1.3, but Mbed TLS rejects it
+ *                   even in TLS 1.2.)
  */
 int mbedtls_ssl_handshake(mbedtls_ssl_context *ssl);
 
diff --git a/library/psa_crypto_slot_management.c b/library/psa_crypto_slot_management.c
index 9850d8c..358c7a2 100644
--- a/library/psa_crypto_slot_management.c
+++ b/library/psa_crypto_slot_management.c
@@ -35,9 +35,9 @@
                       "Empty user key ID range");
 MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_VENDOR_MIN < PSA_KEY_ID_VENDOR_MAX,
                       "Empty vendor key ID range");
-MBEDTLS_STATIC_ASSERT(MBEDTLS_PSA_KEY_ID_BUILTIN_MIN < MBEDTLS_PSA_KEY_ID_BUILTIN_MAX,
+MBEDTLS_STATIC_ASSERT(MBEDTLS_PSA_KEY_ID_BUILTIN_MIN <= MBEDTLS_PSA_KEY_ID_BUILTIN_MAX,
                       "Empty builtin key ID range");
-MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_VOLATILE_MIN < PSA_KEY_ID_VOLATILE_MAX,
+MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_VOLATILE_MIN <= PSA_KEY_ID_VOLATILE_MAX,
                       "Empty volatile key ID range");
 
 MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_USER_MAX < PSA_KEY_ID_VENDOR_MIN ||
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 7495ae3..348c319 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -1830,10 +1830,11 @@
 MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_check_timer(mbedtls_ssl_context *ssl);
 
-void mbedtls_ssl_reset_in_out_pointers(mbedtls_ssl_context *ssl);
+void mbedtls_ssl_reset_in_pointers(mbedtls_ssl_context *ssl);
+void mbedtls_ssl_update_in_pointers(mbedtls_ssl_context *ssl);
+void mbedtls_ssl_reset_out_pointers(mbedtls_ssl_context *ssl);
 void mbedtls_ssl_update_out_pointers(mbedtls_ssl_context *ssl,
                                      mbedtls_ssl_transform *transform);
-void mbedtls_ssl_update_in_pointers(mbedtls_ssl_context *ssl);
 
 MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_session_reset_int(mbedtls_ssl_context *ssl, int partial);
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index dcda1d3..4adaf7d 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -25,6 +25,7 @@
 #include "constant_time_internal.h"
 #include "mbedtls/constant_time.h"
 
+#include <limits.h>
 #include <string.h>
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
@@ -3220,19 +3221,34 @@
 
 int mbedtls_ssl_prepare_handshake_record(mbedtls_ssl_context *ssl)
 {
-    if (ssl->in_msglen < mbedtls_ssl_hs_hdr_len(ssl)) {
-        MBEDTLS_SSL_DEBUG_MSG(1, ("handshake message too short: %" MBEDTLS_PRINTF_SIZET,
-                                  ssl->in_msglen));
-        return MBEDTLS_ERR_SSL_INVALID_RECORD;
-    }
+    if (ssl->badmac_seen_or_in_hsfraglen == 0) {
+        /* The handshake message must at least include the header.
+         * We may not have the full message yet in case of fragmentation.
+         * To simplify the code, we insist on having the header (and in
+         * particular the handshake message length) in the first
+         * fragment. */
+        if (ssl->in_msglen < mbedtls_ssl_hs_hdr_len(ssl)) {
+            MBEDTLS_SSL_DEBUG_MSG(1, ("handshake message too short: %" MBEDTLS_PRINTF_SIZET,
+                                      ssl->in_msglen));
+            return MBEDTLS_ERR_SSL_INVALID_RECORD;
+        }
 
-    ssl->in_hslen = mbedtls_ssl_hs_hdr_len(ssl) + ssl_get_hs_total_len(ssl);
+        ssl->in_hslen = mbedtls_ssl_hs_hdr_len(ssl) + ssl_get_hs_total_len(ssl);
+    }
 
     MBEDTLS_SSL_DEBUG_MSG(3, ("handshake message: msglen ="
                               " %" MBEDTLS_PRINTF_SIZET ", type = %u, hslen = %"
                               MBEDTLS_PRINTF_SIZET,
                               ssl->in_msglen, ssl->in_msg[0], ssl->in_hslen));
 
+    if (ssl->transform_in != NULL) {
+        MBEDTLS_SSL_DEBUG_MSG(4, ("decrypted handshake message:"
+                                  " iv-buf=%d hdr-buf=%d hdr-buf=%d",
+                                  (int) (ssl->in_iv - ssl->in_buf),
+                                  (int) (ssl->in_hdr - ssl->in_buf),
+                                  (int) (ssl->in_msg - ssl->in_buf)));
+    }
+
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
     if (ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM) {
         int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -3292,10 +3308,103 @@
         }
     } else
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
-    /* With TLS we don't handle fragmentation (for now) */
-    if (ssl->in_msglen < ssl->in_hslen) {
-        MBEDTLS_SSL_DEBUG_MSG(1, ("TLS handshake fragmentation not supported"));
-        return MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
+    {
+        unsigned char *const reassembled_record_start =
+            ssl->in_buf + MBEDTLS_SSL_SEQUENCE_NUMBER_LEN;
+        unsigned char *const payload_start =
+            reassembled_record_start + mbedtls_ssl_in_hdr_len(ssl);
+        unsigned char *payload_end = payload_start + ssl->badmac_seen_or_in_hsfraglen;
+        /* How many more bytes we want to have a complete handshake message. */
+        const size_t hs_remain = ssl->in_hslen - ssl->badmac_seen_or_in_hsfraglen;
+        /* How many bytes of the current record are part of the first
+         * handshake message. There may be more handshake messages (possibly
+         * incomplete) in the same record; if so, we leave them after the
+         * current record, and ssl_consume_current_message() will take
+         * care of consuming the next handshake message. */
+        const size_t hs_this_fragment_len =
+            ssl->in_msglen > hs_remain ? hs_remain : ssl->in_msglen;
+        (void) hs_this_fragment_len;
+
+        MBEDTLS_SSL_DEBUG_MSG(3,
+                              ("%s handshake fragment: %" MBEDTLS_PRINTF_SIZET
+                               ", %u..%u of %" MBEDTLS_PRINTF_SIZET,
+                               (ssl->badmac_seen_or_in_hsfraglen != 0 ?
+                                "subsequent" :
+                                hs_this_fragment_len == ssl->in_hslen ?
+                                "sole" :
+                                "initial"),
+                               ssl->in_msglen,
+                               ssl->badmac_seen_or_in_hsfraglen,
+                               ssl->badmac_seen_or_in_hsfraglen +
+                               (unsigned) hs_this_fragment_len,
+                               ssl->in_hslen));
+
+        /* Move the received handshake fragment to have the whole message
+         * (at least the part received so far) in a single segment at a
+         * known offset in the input buffer.
+         * - When receiving a non-initial handshake fragment, append it to
+         *   the initial segment.
+         * - Even the initial handshake fragment is moved, if it was
+         *   encrypted with an explicit IV: decryption leaves the payload
+         *   after the explicit IV, but here we move it to start where the
+         *   IV was.
+         */
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+        size_t const in_buf_len = ssl->in_buf_len;
+#else
+        size_t const in_buf_len = MBEDTLS_SSL_IN_BUFFER_LEN;
+#endif
+        if (payload_end + ssl->in_msglen > ssl->in_buf + in_buf_len) {
+            MBEDTLS_SSL_DEBUG_MSG(1,
+                                  ("Shouldn't happen: no room to move handshake fragment %"
+                                   MBEDTLS_PRINTF_SIZET " from %p to %p (buf=%p len=%"
+                                   MBEDTLS_PRINTF_SIZET ")",
+                                   ssl->in_msglen,
+                                   (void *) ssl->in_msg, (void *) payload_end,
+                                   (void *) ssl->in_buf, in_buf_len));
+            return MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+        }
+        memmove(payload_end, ssl->in_msg, ssl->in_msglen);
+
+        ssl->badmac_seen_or_in_hsfraglen += (unsigned) ssl->in_msglen;
+        payload_end += ssl->in_msglen;
+
+        if (ssl->badmac_seen_or_in_hsfraglen < ssl->in_hslen) {
+            MBEDTLS_SSL_DEBUG_MSG(3, ("Prepare: waiting for more handshake fragments "
+                                      "%u/%" MBEDTLS_PRINTF_SIZET,
+                                      ssl->badmac_seen_or_in_hsfraglen, ssl->in_hslen));
+            ssl->in_hdr = payload_end;
+            ssl->in_msglen = 0;
+            mbedtls_ssl_update_in_pointers(ssl);
+            return MBEDTLS_ERR_SSL_CONTINUE_PROCESSING;
+        } else {
+            ssl->in_msglen = ssl->badmac_seen_or_in_hsfraglen;
+            ssl->badmac_seen_or_in_hsfraglen = 0;
+            ssl->in_hdr = reassembled_record_start;
+            mbedtls_ssl_update_in_pointers(ssl);
+
+            /* Update the record length in the fully reassembled record */
+            if (ssl->in_msglen > 0xffff) {
+                MBEDTLS_SSL_DEBUG_MSG(1,
+                                      ("Shouldn't happen: in_msglen=%"
+                                       MBEDTLS_PRINTF_SIZET " > 0xffff",
+                                       ssl->in_msglen));
+                return MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+            }
+            MBEDTLS_PUT_UINT16_BE(ssl->in_msglen, ssl->in_len, 0);
+
+            size_t record_len = mbedtls_ssl_in_hdr_len(ssl) + ssl->in_msglen;
+            (void) record_len;
+            MBEDTLS_SSL_DEBUG_BUF(4, "reassembled record",
+                                  ssl->in_hdr, record_len);
+            if (ssl->in_hslen < ssl->in_msglen) {
+                MBEDTLS_SSL_DEBUG_MSG(3,
+                                      ("More handshake messages in the record: "
+                                       "%" MBEDTLS_PRINTF_SIZET " + %" MBEDTLS_PRINTF_SIZET,
+                                       ssl->in_hslen,
+                                       ssl->in_msglen - ssl->in_hslen));
+            }
+        }
     }
 
     return 0;
@@ -4640,6 +4749,14 @@
             return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
         }
 
+        if (ssl->badmac_seen_or_in_hsfraglen != 0) {
+            /* Not all handshake fragments have arrived, do not consume. */
+            MBEDTLS_SSL_DEBUG_MSG(3, ("Consume: waiting for more handshake fragments "
+                                      "%u/%" MBEDTLS_PRINTF_SIZET,
+                                      ssl->badmac_seen_or_in_hsfraglen, ssl->in_hslen));
+            return 0;
+        }
+
         /*
          * Get next Handshake message in the current record
          */
@@ -4665,6 +4782,7 @@
             ssl->in_msglen -= ssl->in_hslen;
             memmove(ssl->in_msg, ssl->in_msg + ssl->in_hslen,
                     ssl->in_msglen);
+            MBEDTLS_PUT_UINT16_BE(ssl->in_msglen, ssl->in_len, 0);
 
             MBEDTLS_SSL_DEBUG_BUF(4, "remaining content in record",
                                   ssl->in_msg, ssl->in_msglen);
@@ -4967,10 +5085,12 @@
                     return ret;
                 }
 
-                if (ssl->conf->badmac_limit != 0 &&
-                    ++ssl->badmac_seen >= ssl->conf->badmac_limit) {
-                    MBEDTLS_SSL_DEBUG_MSG(1, ("too many records with bad MAC"));
-                    return MBEDTLS_ERR_SSL_INVALID_MAC;
+                if (ssl->conf->badmac_limit != 0) {
+                    ++ssl->badmac_seen_or_in_hsfraglen;
+                    if (ssl->badmac_seen_or_in_hsfraglen >= ssl->conf->badmac_limit) {
+                        MBEDTLS_SSL_DEBUG_MSG(1, ("too many records with bad MAC"));
+                        return MBEDTLS_ERR_SSL_INVALID_MAC;
+                    }
                 }
 
                 /* As above, invalid records cause
@@ -5028,6 +5148,18 @@
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
+    /* If we're in the middle of a fragmented TLS handshake message,
+     * we don't accept any other message type. For TLS 1.3, the spec forbids
+     * interleaving other message types between handshake fragments. For TLS
+     * 1.2, the spec does not forbid it but we do. */
+    if (ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_STREAM &&
+        ssl->badmac_seen_or_in_hsfraglen != 0 &&
+        ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE) {
+        MBEDTLS_SSL_DEBUG_MSG(1, ("non-handshake message in the middle"
+                                  " of a fragmented handshake message"));
+        return MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE;
+    }
+
     /*
      * Handle particular types of records
      */
@@ -5339,7 +5471,7 @@
     } else
 #endif
     {
-        ssl->in_ctr = ssl->in_hdr - MBEDTLS_SSL_SEQUENCE_NUMBER_LEN;
+        ssl->in_ctr = ssl->in_buf;
         ssl->in_len = ssl->in_hdr + 3;
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
         ssl->in_cid = ssl->in_len;
@@ -5355,24 +5487,35 @@
  * Setup an SSL context
  */
 
-void mbedtls_ssl_reset_in_out_pointers(mbedtls_ssl_context *ssl)
+void mbedtls_ssl_reset_in_pointers(mbedtls_ssl_context *ssl)
+{
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if (ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM) {
+        ssl->in_hdr = ssl->in_buf;
+    } else
+#endif  /* MBEDTLS_SSL_PROTO_DTLS */
+    {
+        ssl->in_hdr = ssl->in_buf + MBEDTLS_SSL_SEQUENCE_NUMBER_LEN;
+    }
+
+    /* Derive other internal pointers. */
+    mbedtls_ssl_update_in_pointers(ssl);
+}
+
+void mbedtls_ssl_reset_out_pointers(mbedtls_ssl_context *ssl)
 {
     /* Set the incoming and outgoing record pointers. */
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
     if (ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM) {
         ssl->out_hdr = ssl->out_buf;
-        ssl->in_hdr  = ssl->in_buf;
     } else
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
     {
         ssl->out_ctr = ssl->out_buf;
-        ssl->out_hdr = ssl->out_buf + 8;
-        ssl->in_hdr  = ssl->in_buf  + 8;
+        ssl->out_hdr = ssl->out_buf + MBEDTLS_SSL_SEQUENCE_NUMBER_LEN;
     }
-
     /* Derive other internal pointers. */
     mbedtls_ssl_update_out_pointers(ssl, NULL /* no transform enabled */);
-    mbedtls_ssl_update_in_pointers(ssl);
 }
 
 /*
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index c773365..7f74248 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -344,12 +344,13 @@
                                    size_t out_buf_new_len)
 {
     int modified = 0;
-    size_t written_in = 0, iv_offset_in = 0, len_offset_in = 0;
+    size_t written_in = 0, iv_offset_in = 0, len_offset_in = 0, hdr_in = 0;
     size_t written_out = 0, iv_offset_out = 0, len_offset_out = 0;
     if (ssl->in_buf != NULL) {
         written_in = ssl->in_msg - ssl->in_buf;
         iv_offset_in = ssl->in_iv - ssl->in_buf;
         len_offset_in = ssl->in_len - ssl->in_buf;
+        hdr_in = ssl->in_hdr - ssl->in_buf;
         if (downsizing ?
             ssl->in_buf_len > in_buf_new_len && ssl->in_left < in_buf_new_len :
             ssl->in_buf_len < in_buf_new_len) {
@@ -381,7 +382,10 @@
     }
     if (modified) {
         /* Update pointers here to avoid doing it twice. */
-        mbedtls_ssl_reset_in_out_pointers(ssl);
+        ssl->in_hdr = ssl->in_buf + hdr_in;
+        mbedtls_ssl_update_in_pointers(ssl);
+        mbedtls_ssl_reset_out_pointers(ssl);
+
         /* Fields below might not be properly updated with record
          * splitting or with CID, so they are manually updated here. */
         ssl->out_msg = ssl->out_buf + written_out;
@@ -1409,7 +1413,8 @@
         goto error;
     }
 
-    mbedtls_ssl_reset_in_out_pointers(ssl);
+    mbedtls_ssl_reset_in_pointers(ssl);
+    mbedtls_ssl_reset_out_pointers(ssl);
 
 #if defined(MBEDTLS_SSL_DTLS_SRTP)
     memset(&ssl->dtls_srtp_info, 0, sizeof(ssl->dtls_srtp_info));
@@ -1474,7 +1479,8 @@
     /* Cancel any possibly running timer */
     mbedtls_ssl_set_timer(ssl, 0);
 
-    mbedtls_ssl_reset_in_out_pointers(ssl);
+    mbedtls_ssl_reset_in_pointers(ssl);
+    mbedtls_ssl_reset_out_pointers(ssl);
 
     /* Reset incoming message parsing */
     ssl->in_offt    = NULL;
@@ -1485,6 +1491,12 @@
     ssl->keep_current_message = 0;
     ssl->transform_in  = NULL;
 
+    /* TLS: reset in_hsfraglen, which is part of message parsing.
+     * DTLS: on a client reconnect, don't reset badmac_seen. */
+    if (!partial) {
+        ssl->badmac_seen_or_in_hsfraglen = 0;
+    }
+
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
     ssl->next_record_offset = 0;
     ssl->in_epoch = 0;
@@ -5014,7 +5026,7 @@
  *  uint8 in_cid<0..2^8-1>      // Connection ID: expected incoming value
  *  uint8 out_cid<0..2^8-1>     // Connection ID: outgoing value to use
  *  // fields from ssl_context
- *  uint32 badmac_seen;         // DTLS: number of records with failing MAC
+ *  uint32 badmac_seen_or_in_hsfraglen;         // DTLS: number of records with failing MAC
  *  uint64 in_window_top;       // DTLS: last validated record seq_num
  *  uint64 in_window;           // DTLS: bitmask for replay protection
  *  uint8 disable_datagram_packing; // DTLS: only one record per datagram
@@ -5156,7 +5168,7 @@
      */
     used += 4;
     if (used <= buf_len) {
-        MBEDTLS_PUT_UINT32_BE(ssl->badmac_seen, p, 0);
+        MBEDTLS_PUT_UINT32_BE(ssl->badmac_seen_or_in_hsfraglen, p, 0);
         p += 4;
     }
 
@@ -5386,7 +5398,7 @@
         return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
     }
 
-    ssl->badmac_seen = MBEDTLS_GET_UINT32_BE(p, 0);
+    ssl->badmac_seen_or_in_hsfraglen = MBEDTLS_GET_UINT32_BE(p, 0);
     p += 4;
 
 #if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
diff --git a/library/ssl_tls12_server.c b/library/ssl_tls12_server.c
index 03722ac..67df428 100644
--- a/library/ssl_tls12_server.c
+++ b/library/ssl_tls12_server.c
@@ -1057,28 +1057,6 @@
         MBEDTLS_SSL_DEBUG_MSG(1, ("bad client hello message"));
         return MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE;
     }
-    {
-        size_t handshake_len = MBEDTLS_GET_UINT24_BE(buf, 1);
-        MBEDTLS_SSL_DEBUG_MSG(3, ("client hello v3, handshake len.: %u",
-                                  (unsigned) handshake_len));
-
-        /* The record layer has a record size limit of 2^14 - 1 and
-         * fragmentation is not supported, so buf[1] should be zero. */
-        if (buf[1] != 0) {
-            MBEDTLS_SSL_DEBUG_MSG(1, ("bad client hello message: %u != 0",
-                                      (unsigned) buf[1]));
-            return MBEDTLS_ERR_SSL_DECODE_ERROR;
-        }
-
-        /* We don't support fragmentation of ClientHello (yet?) */
-        if (msg_len != mbedtls_ssl_hs_hdr_len(ssl) + handshake_len) {
-            MBEDTLS_SSL_DEBUG_MSG(1, ("bad client hello message: %u != %u + %u",
-                                      (unsigned) msg_len,
-                                      (unsigned) mbedtls_ssl_hs_hdr_len(ssl),
-                                      (unsigned) handshake_len));
-            return MBEDTLS_ERR_SSL_DECODE_ERROR;
-        }
-    }
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
     if (ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM) {
diff --git a/programs/ssl/ssl_context_info.c b/programs/ssl/ssl_context_info.c
index 51e8781..b9a0fe8 100644
--- a/programs/ssl/ssl_context_info.c
+++ b/programs/ssl/ssl_context_info.c
@@ -743,6 +743,13 @@
  *  uint8 alpn_chosen_len;
  *  uint8 alpn_chosen<0..2^8-1> // ALPN: negotiated application protocol
  *
+ * Note: In the mbedtls_ssl_context structure, badmac_seen is called
+ * badmac_seen_or_in_hsfraglen since Mbed TLS 3.6.2. The field contains
+ * the badmac_seen value in DTLS, and a handshake parsing intermediate
+ * value in non-DTLS TLS. The value is only meaningful for DTLS and should
+ * not be saved in non-DTLS TLS, so in this program, the context info file
+ * filed remains badmac_seen.
+ *
  * /p ssl   pointer to serialized session
  * /p len   number of bytes in the buffer
  */
diff --git a/programs/ssl/ssl_test_lib.h b/programs/ssl/ssl_test_lib.h
index 9614333..d7fe80f 100644
--- a/programs/ssl/ssl_test_lib.h
+++ b/programs/ssl/ssl_test_lib.h
@@ -243,8 +243,8 @@
  * - free the provided PK context and re-initilize it as an opaque PK context
  *   wrapping the PSA key imported in the above step.
  *
- * \param[in/out] pk    On input the non-opaque PK context which contains the
- *                      key to be wrapped. On output the re-initialized PK
+ * \param[in,out] pk    On input, the non-opaque PK context which contains the
+ *                      key to be wrapped. On output, the re-initialized PK
  *                      context which represents the opaque version of the one
  *                      provided as input.
  * \param[in] psa_alg   The primary algorithm that will be associated to the
diff --git a/scripts/make_generated_files.bat b/scripts/make_generated_files.bat
index 0c15c38..75c2de0 100644
--- a/scripts/make_generated_files.bat
+++ b/scripts/make_generated_files.bat
@@ -28,4 +28,5 @@
 python framework\scripts\generate_psa_tests.py || exit /b 1
 python framework\scripts\generate_test_keys.py --output framework\tests\include\test\test_keys.h || exit /b 1
 python framework\scripts\generate_test_cert_macros.py --output tests\src\test_certs.h || exit /b 1
+python framework\scripts\generate_tls_handshake_tests.py || exit /b 1
 python framework\scripts\generate_tls13_compat_tests.py || exit /b 1
diff --git a/tests/.gitignore b/tests/.gitignore
index 0c58875..10eb873 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -18,6 +18,7 @@
 
 ###START_GENERATED_FILES###
 # Generated source files
+/opt-testcases/handshake-generated.sh
 /opt-testcases/tls13-compat.sh
 /suites/*.generated.data
 /suites/test_suite_config.mbedtls_boolean.data
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 98973c9..aa8ae23 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -124,6 +124,24 @@
             # change too often in ways that don't affect the result
             # ((un)commenting some options).
     )
+
+    add_custom_command(
+        OUTPUT
+            ${CMAKE_CURRENT_SOURCE_DIR}/opt-testcases/handshake-generated.sh
+        WORKING_DIRECTORY
+            ${CMAKE_CURRENT_SOURCE_DIR}/..
+        COMMAND
+            "${MBEDTLS_PYTHON_EXECUTABLE}"
+            "${CMAKE_CURRENT_SOURCE_DIR}/../framework/scripts/generate_tls_handshake_tests.py"
+        DEPENDS
+            ${CMAKE_CURRENT_SOURCE_DIR}/../framework/scripts/mbedtls_framework/tls_test_case.py
+            ${CMAKE_CURRENT_SOURCE_DIR}/../framework/scripts/generate_tls_handshake_tests.py
+    )
+    add_custom_target(handshake-generated.sh
+        DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/opt-testcases/handshake-generated.sh)
+    set_target_properties(handshake-generated.sh PROPERTIES EXCLUDE_FROM_ALL NO)
+    add_dependencies(${ssl_opt_target} handshake-generated.sh)
+
     add_custom_command(
         OUTPUT
             ${ecp_generated_data_files}
diff --git a/tests/Makefile b/tests/Makefile
index dd1af15..1fa5dd1 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -58,6 +58,13 @@
 # Generated files needed to (fully) run ssl-opt.sh
 .PHONY: ssl-opt
 
+opt-testcases/handshake-generated.sh: ../framework/scripts/mbedtls_framework/tls_test_case.py
+opt-testcases/handshake-generated.sh: ../framework/scripts/generate_tls_handshake_tests.py
+	echo "  Gen   $@"
+	$(PYTHON) ../framework/scripts/generate_tls_handshake_tests.py -o $@
+GENERATED_FILES += opt-testcases/handshake-generated.sh
+ssl-opt: opt-testcases/handshake-generated.sh
+
 opt-testcases/tls13-compat.sh: ../framework/scripts/generate_tls13_compat_tests.py
 	echo "  Gen   $@"
 	$(PYTHON) ../framework/scripts/generate_tls13_compat_tests.py -o $@
diff --git a/tests/scripts/check-generated-files.sh b/tests/scripts/check-generated-files.sh
index b61c5ac..088f16f 100755
--- a/tests/scripts/check-generated-files.sh
+++ b/tests/scripts/check-generated-files.sh
@@ -135,6 +135,7 @@
     check scripts/generate_query_config.pl programs/test/query_config.c
     check scripts/generate_features.pl library/version_features.c
     check framework/scripts/generate_ssl_debug_helpers.py library/ssl_debug_helpers_generated.c
+    check framework/scripts/generate_tls_handshake_tests.py tests/opt-testcases/handshake-generated.sh
     check framework/scripts/generate_tls13_compat_tests.py tests/opt-testcases/tls13-compat.sh
     check framework/scripts/generate_test_cert_macros.py tests/src/test_certs.h
     # generate_visualc_files enumerates source files (library/*.c). It doesn't
diff --git a/tests/ssl-opt.sh b/tests/ssl-opt.sh
index 0376018..fdbe0a9 100755
--- a/tests/ssl-opt.sh
+++ b/tests/ssl-opt.sh
@@ -14457,6 +14457,20 @@
             -c "Handshake was completed" \
             -s "dumping .client hello, compression. (2 bytes)"
 
+# Handshake defragmentation testing
+
+# Most test cases are in opt-testcases/handshake-generated.sh
+
+requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_2
+requires_certificate_authentication
+run_test    "Handshake defragmentation on server: len=32, TLS 1.2 ClientHello" \
+            "$P_SRV debug_level=4 force_version=tls12 auth_mode=required" \
+            "$O_NEXT_CLI -tls1_2 -split_send_frag 32 -cert $DATA_FILES_PATH/server5.crt -key $DATA_FILES_PATH/server5.key" \
+            1 \
+            -s "The SSL configuration is tls12 only" \
+            -s "bad client hello message" \
+            -s "SSL - A message could not be parsed due to a syntactic error"
+
 # Test heap memory usage after handshake
 requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_2
 requires_config_enabled MBEDTLS_MEMORY_DEBUG