diff --git a/src/classic/a2dp_source.c b/src/classic/a2dp_source.c
index 74370819f..e8718883e 100644
--- a/src/classic/a2dp_source.c
+++ b/src/classic/a2dp_source.c
@@ -422,7 +422,6 @@ static void a2dp_source_packet_handler_internal(uint8_t packet_type, uint16_t ch
                     configuration.min_bitpool_value  = avdtp_choose_sbc_min_bitpool_value(stream_endpoint, avdtp_subevent_signaling_media_codec_sbc_capability_get_min_bitpool_value(packet));
 
                     // and pre-select this endpoint
-                    stream_endpoint->sep.in_use = 1;
                     local_seid = avdtp_stream_endpoint_seid(stream_endpoint);
                     remote_seid = avdtp_subevent_signaling_media_codec_sbc_capability_get_remote_seid(packet);
                     a2dp_source_set_config_sbc(cid, local_seid, remote_seid, &configuration);
diff --git a/src/classic/avdtp_acceptor.c b/src/classic/avdtp_acceptor.c
index 23823ecca..770782569 100644
--- a/src/classic/avdtp_acceptor.c
+++ b/src/classic/avdtp_acceptor.c
@@ -101,6 +101,13 @@ avdtp_acceptor_handle_configuration_command(avdtp_connection_t *connection, int
     sep.configured_service_categories = avdtp_unpack_service_capabilities(connection, connection->acceptor_signaling_packet.signal_identifier, &sep.configuration, connection->acceptor_signaling_packet.command+offset, packet_size-offset);
     sep.in_use = 1;
 
+    // test if sep already in use
+    if (stream_endpoint->sep.in_use != 0){
+        log_info("stream endpoint already in use");
+        connection->error_code = AVDTP_ERROR_CODE_SEP_IN_USE;
+        connection->reject_service_category = 0;
+    }
+
     // let application validate media configuration as well
     if (connection->error_code == 0){
         if ((sep.configured_service_categories & (1 << AVDTP_MEDIA_CODEC)) != 0){
@@ -150,6 +157,9 @@ avdtp_acceptor_handle_configuration_command(avdtp_connection_t *connection, int
         stream_endpoint->remote_sep = sep;
         log_info("add remote seid %d", stream_endpoint->remote_sep.seid);
     }
+    
+    // mark as in_use
+    stream_endpoint->sep.in_use = 1;
 
 	// if media codec configuration set, copy configuration and emit event
 	if ((sep.configured_service_categories & (1 << AVDTP_MEDIA_CODEC)) != 0){
diff --git a/src/classic/avdtp_initiator.c b/src/classic/avdtp_initiator.c
index fd2276878..d8c4ee6ba 100644
--- a/src/classic/avdtp_initiator.c
+++ b/src/classic/avdtp_initiator.c
@@ -171,6 +171,7 @@ void avdtp_initiator_stream_config_subsm(avdtp_connection_t *connection, uint8_t
                     sep.in_use = 1;
                     
                     stream_endpoint->state = AVDTP_STREAM_ENDPOINT_CONFIGURED;
+                    stream_endpoint->sep.in_use = 1;
                     stream_endpoint->remote_sep = sep;
                     stream_endpoint->connection = connection;
                     connection->configuration_state = AVDTP_CONFIGURATION_STATE_LOCAL_CONFIGURED;