diff --git a/platform/cc2538dk/contiki-conf.h b/platform/cc2538dk/contiki-conf.h
index d1a10811f..64179b983 100644
--- a/platform/cc2538dk/contiki-conf.h
+++ b/platform/cc2538dk/contiki-conf.h
@@ -64,6 +64,16 @@ typedef uint32_t rtimer_clock_t;
 #endif
 /** @} */
 /*---------------------------------------------------------------------------*/
+/**
+ * \name CC2538 System Control configuration
+ *
+ * @{
+ */
+#ifndef SYS_CTRL_CONF_OSC32K_USE_XTAL
+#define SYS_CTRL_CONF_OSC32K_USE_XTAL   1 /**< Use the on-board 32.768-kHz crystal */
+#endif
+/** @} */
+/*---------------------------------------------------------------------------*/
 /**
  * \name Watchdog Timer configuration
  *
diff --git a/platform/openmote-cc2538/contiki-conf.h b/platform/openmote-cc2538/contiki-conf.h
index 543d3a5e5..90cc6d648 100644
--- a/platform/openmote-cc2538/contiki-conf.h
+++ b/platform/openmote-cc2538/contiki-conf.h
@@ -102,7 +102,16 @@ typedef uint32_t rtimer_clock_t;
 #define FLASH_CCA_CONF_BOOTLDR_BACKDOOR_ACTIVE_HIGH 0 /**< A logic low level activates the boot loader */
 #endif
 /** @} */
-
+/*---------------------------------------------------------------------------*/
+/**
+ * \name CC2538 System Control configuration
+ *
+ * @{
+ */
+#ifndef SYS_CTRL_CONF_OSC32K_USE_XTAL
+#define SYS_CTRL_CONF_OSC32K_USE_XTAL   1 /**< Use the on-board 32.768-kHz crystal */
+#endif
+/** @} */
 /*---------------------------------------------------------------------------*/
 /**
  * \name CFS configuration
diff --git a/platform/zoul/contiki-conf.h b/platform/zoul/contiki-conf.h
index 6bdae897a..bf9754730 100644
--- a/platform/zoul/contiki-conf.h
+++ b/platform/zoul/contiki-conf.h
@@ -100,7 +100,16 @@ typedef uint32_t rtimer_clock_t;
 #define FLASH_CCA_CONF_BOOTLDR_BACKDOOR_ACTIVE_HIGH 0 /**< A logic low level activates the boot loader */
 #endif
 /** @} */
-
+/*---------------------------------------------------------------------------*/
+/**
+ * \name CC2538 System Control configuration
+ *
+ * @{
+ */
+#ifndef SYS_CTRL_CONF_OSC32K_USE_XTAL
+#define SYS_CTRL_CONF_OSC32K_USE_XTAL   1 /**< Use the on-board 32.768-kHz crystal */
+#endif
+/** @} */
 /*---------------------------------------------------------------------------*/
 /**
  * \name CFS configuration