diff --git a/include/zephyr/bluetooth/services/cts.h b/include/zephyr/bluetooth/services/cts.h
index 46fb7808cc4ee..5b1c780f68615 100644
--- a/include/zephyr/bluetooth/services/cts.h
+++ b/include/zephyr/bluetooth/services/cts.h
@@ -16,7 +16,6 @@
  */
 
 #include <stdint.h>
-#include <zephyr/posix/time.h>
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/subsys/bluetooth/services/cts.c b/subsys/bluetooth/services/cts.c
index ce72f7728e019..d5744bc5a2480 100644
--- a/subsys/bluetooth/services/cts.c
+++ b/subsys/bluetooth/services/cts.c
@@ -7,9 +7,17 @@
  *
  * SPDX-License-Identifier: Apache-2.0
  */
+
+#undef _POSIX_C_SOURCE
+#define _POSIX_C_SOURCE 200809L /* To get gmtime_r()'s prototype */
+
+#ifdef CONFIG_BT_CTS_HELPER_API
+#include <time.h>
+#include <zephyr/sys/timeutil.h>
+#endif
+
 #include <stdbool.h>
 #include <zephyr/sys/byteorder.h>
-#include <zephyr/posix/time.h>
 
 #include <zephyr/bluetooth/conn.h>
 #include <zephyr/bluetooth/gatt.h>
@@ -26,9 +34,6 @@ static const struct bt_cts_cb *cts_cb;
 
 #ifdef CONFIG_BT_CTS_HELPER_API
 
-#include <time.h>
-#include <zephyr/sys/timeutil.h>
-
 int bt_cts_time_to_unix_ms(const struct bt_cts_time_format *ct_time, int64_t *unix_ms)
 {
 	struct tm date_time;