diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 97c00e256..80da3ac1a 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -1203,6 +1203,9 @@ void mbedtls_ssl_send_flight_completed( mbedtls_ssl_context *ssl );
 void mbedtls_ssl_recv_flight_completed( mbedtls_ssl_context *ssl );
 int mbedtls_ssl_resend( mbedtls_ssl_context *ssl );
 int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl );
+#if defined(MBEDTLS_IMMEDIATE_TRANSMISSION)
+void mbedtls_ssl_immediate_flight_done( mbedtls_ssl_context *ssl );
+#endif
 #endif
 
 /* Visible for testing purposes only */
diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 08d5a7117..7f69b6242 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -1141,11 +1141,17 @@ static int ssl_write_client_hello( mbedtls_ssl_context *ssl )
     }
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
-    if( MBEDTLS_SSL_TRANSPORT_IS_DTLS( ssl->conf->transport ) &&
-        ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
+    if( MBEDTLS_SSL_TRANSPORT_IS_DTLS( ssl->conf->transport ) )
     {
-        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit", ret );
-        return( ret );
+#if defined(MBEDTLS_IMMEDIATE_TRANSMISSION)
+        mbedtls_ssl_immediate_flight_done( ssl );
+#else
+        if( ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit", ret );
+            return( ret );
+        }
+#endif
     }
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 389a24e48..ce92f98dc 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -2743,11 +2743,17 @@ static int ssl_write_hello_verify_request( mbedtls_ssl_context *ssl )
     }
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
-    if( MBEDTLS_SSL_TRANSPORT_IS_DTLS( ssl->conf->transport ) &&
-        ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
+    if( MBEDTLS_SSL_TRANSPORT_IS_DTLS( ssl->conf->transport ) )
     {
-        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit", ret );
-        return( ret );
+#if defined(MBEDTLS_IMMEDIATE_TRANSMISSION)
+        mbedtls_ssl_immediate_flight_done( ssl );
+#else
+        if( ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit", ret );
+            return( ret );
+        }
+#endif
     }
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
@@ -3802,11 +3808,17 @@ static int ssl_write_server_hello_done( mbedtls_ssl_context *ssl )
     }
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
-    if( MBEDTLS_SSL_TRANSPORT_IS_DTLS( ssl->conf->transport ) &&
-        ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
+    if( MBEDTLS_SSL_TRANSPORT_IS_DTLS( ssl->conf->transport ) )
     {
-        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit", ret );
-        return( ret );
+#if defined(MBEDTLS_IMMEDIATE_TRANSMISSION)
+        mbedtls_ssl_immediate_flight_done( ssl );
+#else
+        if( ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit", ret );
+            return( ret );
+        }
+#endif
     }
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 038e581d5..f20faf92a 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -4360,6 +4360,131 @@ int mbedtls_ssl_flush_output( mbedtls_ssl_context *ssl )
  * Functions to handle the DTLS retransmission state machine
  */
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
+static int ssl_swap_epochs( mbedtls_ssl_context *ssl );
+
+static int mbedtls_ssl_flight_transmit_msg( mbedtls_ssl_context *ssl, mbedtls_ssl_flight_item *msg )
+{
+    size_t max_frag_len;
+    int ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
+    int const is_retransmitting =
+            ( ssl->handshake->retransmit_state == MBEDTLS_SSL_RETRANS_SENDING );
+    int const is_finished =
+        ( msg->type == MBEDTLS_SSL_MSG_HANDSHAKE &&
+          msg->p[0] == MBEDTLS_SSL_HS_FINISHED );
+
+    uint8_t const force_flush = ssl->disable_datagram_packing == 1 ?
+        SSL_FORCE_FLUSH : SSL_DONT_FORCE_FLUSH;
+
+    /* Swap epochs before sending Finished: we can't do it after
+     * sending ChangeCipherSpec, in case write returns WANT_READ.
+     * Must be done before copying, may change out_msg pointer */
+    if( is_retransmitting && is_finished && ssl->handshake->cur_msg_p == ( msg->p + 12 ) )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "swap epochs to send finished message" ) );
+        if( ( ret = ssl_swap_epochs( ssl ) ) != 0 )
+            return( ret );
+    }
+
+    ret = ssl_get_remaining_payload_in_datagram( ssl );
+    if( ret < 0 )
+        return( ret );
+    max_frag_len = (size_t) ret;
+
+    /* CCS is copied as is, while HS messages may need fragmentation */
+    if( msg->type == MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC )
+    {
+        if( max_frag_len == 0 )
+        {
+            if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
+                return( ret );
+
+            return( 0 );
+        }
+
+        mbedtls_platform_memcpy( ssl->out_msg, msg->p, msg->len );
+        ssl->out_msglen  = msg->len;
+        ssl->out_msgtype = msg->type;
+
+        /* Update position inside current message */
+        ssl->handshake->cur_msg_p += msg->len;
+    }
+    else
+    {
+        const unsigned char * const p = ssl->handshake->cur_msg_p;
+        const size_t hs_len = msg->len - 12;
+        const size_t frag_off = p - ( msg->p + 12 );
+        const size_t rem_len = hs_len - frag_off;
+        size_t cur_hs_frag_len, max_hs_frag_len;
+
+        if( ( max_frag_len < 12 ) || ( max_frag_len == 12 && hs_len != 0 ) )
+        {
+            if( is_finished && is_retransmitting )
+            {
+                if( ( ret = ssl_swap_epochs( ssl ) ) != 0 )
+                    return( ret );
+            }
+
+            if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
+                return( ret );
+
+            return( 0 );
+        }
+        max_hs_frag_len = max_frag_len - 12;
+
+        cur_hs_frag_len = rem_len > max_hs_frag_len ?
+            max_hs_frag_len : rem_len;
+
+        if( frag_off == 0 && cur_hs_frag_len != hs_len )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 2, ( "fragmenting handshake message (%u > %u)",
+                                        (unsigned) cur_hs_frag_len,
+                                        (unsigned) max_hs_frag_len ) );
+        }
+
+        /* Messages are stored with handshake headers as if not fragmented,
+         * copy beginning of headers then fill fragmentation fields.
+         * Handshake headers: type(1) len(3) seq(2) f_off(3) f_len(3) */
+        mbedtls_platform_memcpy( ssl->out_msg, msg->p, 6 );
+
+        (void)mbedtls_platform_put_uint24_be( &ssl->out_msg[6], frag_off );
+        (void)mbedtls_platform_put_uint24_be( &ssl->out_msg[9],
+                                              cur_hs_frag_len );
+
+        MBEDTLS_SSL_DEBUG_BUF( 3, "handshake header", ssl->out_msg, 12 );
+
+        /* Copy the handshake message content and set records fields */
+        mbedtls_platform_memcpy( ssl->out_msg + 12, p, cur_hs_frag_len );
+        ssl->out_msglen = cur_hs_frag_len + 12;
+        ssl->out_msgtype = msg->type;
+
+        /* Update position inside current message */
+        ssl->handshake->cur_msg_p += cur_hs_frag_len;
+    }
+
+    /* If done with the current message move to the next one if any */
+    if( ssl->handshake->cur_msg_p >= msg->p + msg->len )
+    {
+        if( msg->next != NULL )
+        {
+            ssl->handshake->cur_msg = msg->next;
+            ssl->handshake->cur_msg_p = msg->next->p + 12;
+        }
+        else
+        {
+            ssl->handshake->cur_msg = NULL;
+            ssl->handshake->cur_msg_p = NULL;
+        }
+    }
+
+    /* Actually send the message out */
+    if( ( ret = mbedtls_ssl_write_record( ssl, force_flush ) ) != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_record", ret );
+        return( ret );
+    }
+    return( ret );
+}
+
 /*
  * Append current handshake message to current outgoing flight
  */
@@ -4402,6 +4527,21 @@ static int ssl_flight_append( mbedtls_ssl_context *ssl )
         cur->next = msg;
     }
 
+#if defined(MBEDTLS_IMMEDIATE_TRANSMISSION)
+    ssl->handshake->cur_msg = msg;
+    ssl->handshake->cur_msg_p = msg->p + 12;
+    {
+        int ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
+        while( ssl->handshake->cur_msg != NULL )
+        {
+            if( ( ret = mbedtls_ssl_flight_transmit_msg( ssl, ssl->handshake->cur_msg ) ) != 0 )
+            {
+                MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit_msg", ret );
+                return( ret );
+            }
+        }
+    }
+#endif
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= ssl_flight_append" ) );
     return( 0 );
 }
@@ -4491,6 +4631,24 @@ int mbedtls_ssl_resend( mbedtls_ssl_context *ssl )
     return( ret );
 }
 
+#if defined(MBEDTLS_IMMEDIATE_TRANSMISSION)
+void mbedtls_ssl_immediate_flight_done( mbedtls_ssl_context *ssl )
+{
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> mbedtls_ssl_immediate_flight_done" ) );
+
+    /* Update state and set timer */
+    if( ssl->state == MBEDTLS_SSL_HANDSHAKE_OVER )
+        ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_FINISHED;
+    else
+    {
+        ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_WAITING;
+        ssl_set_timer( ssl, ssl->handshake->retransmit_timeout );
+    }
+
+    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= mbedtls_ssl_immediate_flight_done" ) );
+}
+#endif
+
 /*
  * Transmit or retransmit the current flight of messages.
  *
@@ -4507,138 +4665,19 @@ int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl )
     {
         MBEDTLS_SSL_DEBUG_MSG( 2, ( "initialise flight transmission" ) );
 
-#if defined(MBEDTLS_IMMEDIATE_TRANSMISSION)
-        ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_SENDING;
-
-        return( 0 );
-#else
-
         ssl->handshake->cur_msg = ssl->handshake->flight;
         ssl->handshake->cur_msg_p = ssl->handshake->flight->p + 12;
         if( ( ret = ssl_swap_epochs( ssl ) ) != 0 )
             return( ret );
 
         ssl->handshake->retransmit_state = MBEDTLS_SSL_RETRANS_SENDING;
-#endif /* MBEDTLS_IMMEDIATE_TRANSMISSION */
     }
 
     while( ssl->handshake->cur_msg != NULL )
     {
-        size_t max_frag_len;
-        const mbedtls_ssl_flight_item * const cur = ssl->handshake->cur_msg;
-
-        int const is_finished =
-            ( cur->type == MBEDTLS_SSL_MSG_HANDSHAKE &&
-              cur->p[0] == MBEDTLS_SSL_HS_FINISHED );
-
-        uint8_t const force_flush = ssl->disable_datagram_packing == 1 ?
-            SSL_FORCE_FLUSH : SSL_DONT_FORCE_FLUSH;
-
-        /* Swap epochs before sending Finished: we can't do it after
-         * sending ChangeCipherSpec, in case write returns WANT_READ.
-         * Must be done before copying, may change out_msg pointer */
-        if( is_finished && ssl->handshake->cur_msg_p == ( cur->p + 12 ) )
+        if( ( ret = mbedtls_ssl_flight_transmit_msg( ssl, ssl->handshake->cur_msg ) ) != 0 )
         {
-            MBEDTLS_SSL_DEBUG_MSG( 2, ( "swap epochs to send finished message" ) );
-            if( ( ret = ssl_swap_epochs( ssl ) ) != 0 )
-                return( ret );
-        }
-
-        ret = ssl_get_remaining_payload_in_datagram( ssl );
-        if( ret < 0 )
-            return( ret );
-        max_frag_len = (size_t) ret;
-
-        /* CCS is copied as is, while HS messages may need fragmentation */
-        if( cur->type == MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC )
-        {
-            if( max_frag_len == 0 )
-            {
-                if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
-                    return( ret );
-
-                continue;
-            }
-
-            mbedtls_platform_memcpy( ssl->out_msg, cur->p, cur->len );
-            ssl->out_msglen  = cur->len;
-            ssl->out_msgtype = cur->type;
-
-            /* Update position inside current message */
-            ssl->handshake->cur_msg_p += cur->len;
-        }
-        else
-        {
-            const unsigned char * const p = ssl->handshake->cur_msg_p;
-            const size_t hs_len = cur->len - 12;
-            const size_t frag_off = p - ( cur->p + 12 );
-            const size_t rem_len = hs_len - frag_off;
-            size_t cur_hs_frag_len, max_hs_frag_len;
-
-            if( ( max_frag_len < 12 ) || ( max_frag_len == 12 && hs_len != 0 ) )
-            {
-                if( is_finished )
-                {
-                    if( ( ret = ssl_swap_epochs( ssl ) ) != 0 )
-                        return( ret );
-                }
-
-                if( ( ret = mbedtls_ssl_flush_output( ssl ) ) != 0 )
-                    return( ret );
-
-                continue;
-            }
-            max_hs_frag_len = max_frag_len - 12;
-
-            cur_hs_frag_len = rem_len > max_hs_frag_len ?
-                max_hs_frag_len : rem_len;
-
-            if( frag_off == 0 && cur_hs_frag_len != hs_len )
-            {
-                MBEDTLS_SSL_DEBUG_MSG( 2, ( "fragmenting handshake message (%u > %u)",
-                                            (unsigned) cur_hs_frag_len,
-                                            (unsigned) max_hs_frag_len ) );
-            }
-
-            /* Messages are stored with handshake headers as if not fragmented,
-             * copy beginning of headers then fill fragmentation fields.
-             * Handshake headers: type(1) len(3) seq(2) f_off(3) f_len(3) */
-            mbedtls_platform_memcpy( ssl->out_msg, cur->p, 6 );
-
-            (void)mbedtls_platform_put_uint24_be( &ssl->out_msg[6], frag_off );
-            (void)mbedtls_platform_put_uint24_be( &ssl->out_msg[9],
-                                                  cur_hs_frag_len );
-
-            MBEDTLS_SSL_DEBUG_BUF( 3, "handshake header", ssl->out_msg, 12 );
-
-            /* Copy the handshake message content and set records fields */
-            mbedtls_platform_memcpy( ssl->out_msg + 12, p, cur_hs_frag_len );
-            ssl->out_msglen = cur_hs_frag_len + 12;
-            ssl->out_msgtype = cur->type;
-
-            /* Update position inside current message */
-            ssl->handshake->cur_msg_p += cur_hs_frag_len;
-        }
-
-        /* If done with the current message move to the next one if any */
-        if( ssl->handshake->cur_msg_p >= cur->p + cur->len )
-        {
-            if( cur->next != NULL )
-            {
-                ssl->handshake->cur_msg = cur->next;
-                ssl->handshake->cur_msg_p = cur->next->p + 12;
-            }
-            else
-            {
-                ssl->handshake->cur_msg = NULL;
-                ssl->handshake->cur_msg_p = NULL;
-            }
-        }
-
-        /* Actually send the message out */
-        if( ( ret = mbedtls_ssl_write_record( ssl, force_flush ) ) != 0 )
-        {
-            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_write_record", ret );
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit_msg", ret );
             return( ret );
         }
     }
@@ -4657,7 +4696,7 @@ int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl )
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= mbedtls_ssl_flight_transmit" ) );
 
-    return( 0 );
+    return( ret );
 }
 
 /*
@@ -4868,14 +4907,6 @@ int mbedtls_ssl_write_handshake_msg( mbedtls_ssl_context *ssl )
         ! ( ssl->out_msgtype == MBEDTLS_SSL_MSG_HANDSHAKE &&
             hs_type          == MBEDTLS_SSL_HS_HELLO_REQUEST ) )
     {
-#if defined(MBEDTLS_IMMEDIATE_TRANSMISSION)
-        if( ( ret = mbedtls_ssl_write_record( ssl, SSL_FORCE_FLUSH ) ) != 0 )
-        {
-            MBEDTLS_SSL_DEBUG_RET( 1, "ssl_write_record", ret );
-            return( ret );
-        }
-#endif /* MBEDTLS_IMMEDIATE_TRANSMISSION */
-
         if( ( ret = ssl_flight_append( ssl ) ) != 0 )
         {
             MBEDTLS_SSL_DEBUG_RET( 1, "ssl_flight_append", ret );
@@ -8707,13 +8738,19 @@ int mbedtls_ssl_write_finished( mbedtls_ssl_context *ssl )
     }
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
-    if( MBEDTLS_SSL_TRANSPORT_IS_DTLS( ssl->conf->transport ) &&
-        ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
+    if( MBEDTLS_SSL_TRANSPORT_IS_DTLS( ssl->conf->transport ) )
     {
-        MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit", ret );
-        return( ret );
-    }
+#if defined(MBEDTLS_IMMEDIATE_TRANSMISSION)
+        mbedtls_ssl_immediate_flight_done( ssl );
+#else
+        if( ( ret = mbedtls_ssl_flight_transmit( ssl ) ) != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ssl_flight_transmit", ret );
+            return( ret );
+        }
 #endif
+    }
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write finished" ) );