diff --git a/src/plugins/relay/api/relay-api-msg.c b/src/plugins/relay/api/relay-api-msg.c
index 507fc1a12..eded094ba 100644
--- a/src/plugins/relay/api/relay-api-msg.c
+++ b/src/plugins/relay/api/relay-api-msg.c
@@ -59,15 +59,11 @@
 
 #define MSG_ADD_HDATA_TIME_USEC(__json_name,                            \
                                 __var_name, __var_name_usec)            \
-    time_value = weechat_hdata_time (hdata, pointer, __var_name);       \
-    local_time = localtime (&time_value);                               \
-    time_value -= local_time->tm_gmtoff;                                \
-    local_time = localtime (&time_value);                               \
-    tv.tv_sec = mktime (local_time);                                    \
+    tv.tv_sec = weechat_hdata_time (hdata, pointer, __var_name);        \
     tv.tv_usec = weechat_hdata_integer (hdata, pointer,                 \
                                         __var_name_usec);               \
     weechat_util_strftimeval (str_time, sizeof (str_time),              \
-                              "%FT%T.%fZ", &tv);                        \
+                              "%@%FT%T.%fZ", &tv);                      \
     MSG_ADD_STR_BUF(__json_name, str_time);
 
 #define MSG_ADD_HDATA_STR(__json_name, __var_name)                      \
@@ -489,9 +485,7 @@ relay_api_msg_line_data_to_json (struct t_gui_line_data *line_data,
     const char *ptr_string;
     char *string, str_time[256], str_var[64];
     int i, tags_count;
-    time_t time_value;
     struct timeval tv;
-    struct tm *local_time;
 
     hdata = relay_hdata_line_data;
     pointer = line_data;
@@ -794,9 +788,7 @@ relay_api_msg_hotlist_to_json (struct t_gui_hotlist *hotlist)
     struct t_gui_hotlist *pointer;
     struct t_gui_buffer *buffer;
     cJSON *json, *json_count;
-    time_t time_value;
     struct timeval tv;
-    struct tm *local_time;
     char str_time[256], str_key[32];
     int i, array_size;
     long long buffer_id;
diff --git a/tests/unit/plugins/relay/api/test-relay-api-msg.cpp b/tests/unit/plugins/relay/api/test-relay-api-msg.cpp
index a89b820fb..46b99df4f 100644
--- a/tests/unit/plugins/relay/api/test-relay-api-msg.cpp
+++ b/tests/unit/plugins/relay/api/test-relay-api-msg.cpp
@@ -419,12 +419,12 @@ TEST(RelayApiMsg, LinesToJson)
     gmtime_r (&(gui_buffers->own_lines->last_line->prev_line->data->date), &gm_time);
     tv.tv_sec = mktime (&gm_time);
     tv.tv_usec = gui_buffers->own_lines->last_line->prev_line->data->date_usec;
-    util_strftimeval (str_date, sizeof (str_date), "%FT%T.%fZ", &tv);
+    util_strftimeval (str_date, sizeof (str_date), "%@%FT%T.%fZ", &tv);
     WEE_CHECK_OBJ_STR(str_date, json_line, "date");
     gmtime_r (&(gui_buffers->own_lines->last_line->prev_line->data->date_printed), &gm_time);
     tv.tv_sec = mktime (&gm_time);
     tv.tv_usec = gui_buffers->own_lines->last_line->prev_line->data->date_usec_printed;
-    util_strftimeval (str_date, sizeof (str_date), "%FT%T.%fZ", &tv);
+    util_strftimeval (str_date, sizeof (str_date), "%@%FT%T.%fZ", &tv);
     WEE_CHECK_OBJ_STR(str_date, json_line, "date_printed");
     WEE_CHECK_OBJ_BOOL(0, json_line, "highlight");
     WEE_CHECK_OBJ_STR("nick1", json_line, "prefix");
@@ -455,12 +455,12 @@ TEST(RelayApiMsg, LinesToJson)
     gmtime_r (&(gui_buffers->own_lines->last_line->data->date), &gm_time);
     tv.tv_sec = mktime (&gm_time);
     tv.tv_usec = gui_buffers->own_lines->last_line->data->date_usec;
-    util_strftimeval (str_date, sizeof (str_date), "%FT%T.%fZ", &tv);
+    util_strftimeval (str_date, sizeof (str_date), "%@%FT%T.%fZ", &tv);
     WEE_CHECK_OBJ_STR(str_date, json_line, "date");
     gmtime_r (&(gui_buffers->own_lines->last_line->data->date_printed), &gm_time);
     tv.tv_sec = mktime (&gm_time);
     tv.tv_usec = gui_buffers->own_lines->last_line->data->date_usec_printed;
-    util_strftimeval (str_date, sizeof (str_date), "%FT%T.%fZ", &tv);
+    util_strftimeval (str_date, sizeof (str_date), "%@%FT%T.%fZ", &tv);
     WEE_CHECK_OBJ_STR(str_date, json_line, "date_printed");
     WEE_CHECK_OBJ_BOOL(0, json_line, "highlight");
     WEE_CHECK_OBJ_STR("", json_line, "prefix");
@@ -626,7 +626,7 @@ TEST(RelayApiMsg, HotlistToJson)
     gmtime_r (&time_value, &gm_time);
     tv.tv_sec = mktime (&gm_time);
     tv.tv_usec = hdata_integer (relay_hdata_hotlist, gui_hotlist, "time_usec");
-    util_strftimeval (str_date, sizeof (str_date), "%FT%T.%fZ", &tv);
+    util_strftimeval (str_date, sizeof (str_date), "%@%FT%T.%fZ", &tv);
     WEE_CHECK_OBJ_STR(str_date, json, "date");
     WEE_CHECK_OBJ_NUM(gui_buffers->id, json, "buffer_id");
     json_count = cJSON_GetObjectItem (json, "count");