diff --git a/boards/airfy-beacon/include/periph_conf.h b/boards/airfy-beacon/include/periph_conf.h
index 16de55f925..bda397d326 100644
--- a/boards/airfy-beacon/include/periph_conf.h
+++ b/boards/airfy-beacon/include/periph_conf.h
@@ -14,6 +14,7 @@
  * @brief       Peripheral MCU configuration for the Airfy Beacon board
  *
  * @author      Christian Mehlis <mehlis@inf.fu-berlin.de>
+ * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
  */
 
 #ifndef __PERIPH_CONF_H
@@ -23,6 +24,19 @@
  extern "C" {
 #endif
 
+/**
+ * @name Clock configuration
+ *
+ * @note: the radio will not work with the internal RC oscillator!
+ *
+ * @{
+ */
+#define CLOCK_CORECLOCK     (16000000U)     /* fixed for all NRF51822 */
+#define CLOCK_CRYSTAL       (16U)           /* set to  0: internal RC oscillator
+                                                      16: 16MHz crystal
+                                                      32: 32MHz crystal */
+/** @} */
+
 /**
  * @name Timer configuration
  * @{
diff --git a/boards/pca10000/include/periph_conf.h b/boards/pca10000/include/periph_conf.h
index 3c18debc8c..73d6d75f9b 100644
--- a/boards/pca10000/include/periph_conf.h
+++ b/boards/pca10000/include/periph_conf.h
@@ -25,6 +25,19 @@
 extern "C" {
 #endif
 
+/**
+ * @name Clock configuration
+ *
+ * @note: the radio will not work with the internal RC oscillator!
+ *
+ * @{
+ */
+#define CLOCK_CORECLOCK     (16000000U)     /* fixed for all NRF51822 */
+#define CLOCK_CRYSTAL       (16U)           /* set to  0: internal RC oscillator
+                                                      16: 16MHz crystal
+                                                      32: 32MHz crystal */
+/** @} */
+
 /**
  * @name Timer configuration
  * @{
diff --git a/boards/pca10005/include/periph_conf.h b/boards/pca10005/include/periph_conf.h
index 4d145bb3dc..a08d2fc358 100644
--- a/boards/pca10005/include/periph_conf.h
+++ b/boards/pca10005/include/periph_conf.h
@@ -25,6 +25,19 @@
 extern "C" {
 #endif
 
+/**
+ * @name Clock configuration
+ *
+ * @note: the radio will not work with the internal RC oscillator!
+ *
+ * @{
+ */
+#define CLOCK_CORECLOCK     (16000000U)     /* fixed for all NRF51822 */
+#define CLOCK_CRYSTAL       (16U)           /* set to  0: internal RC oscillator
+                                                      16: 16MHz crystal
+                                                      32: 32MHz crystal */
+/** @} */
+
 /**
  * @name Timer configuration
  * @{
diff --git a/boards/yunjia-nrf51822/include/periph_conf.h b/boards/yunjia-nrf51822/include/periph_conf.h
index 38a5a4a38c..5e19665cc4 100644
--- a/boards/yunjia-nrf51822/include/periph_conf.h
+++ b/boards/yunjia-nrf51822/include/periph_conf.h
@@ -23,6 +23,19 @@
 extern "C" {
 #endif
 
+/**
+ * @name Clock configuration
+ *
+ * @note: the radio will not work with the internal RC oscillator!
+ *
+ * @{
+ */
+#define CLOCK_CORECLOCK     (16000000U)     /* fixed for all NRF51822 */
+#define CLOCK_CRYSTAL       (16U)           /* set to  0: internal RC oscillator
+                                                      16: 16MHz crystal
+                                                      32: 32MHz crystal */
+/** @} */
+
 /**
  * @name Timer configuration
  * @{
diff --git a/cpu/nrf51822/cpu.c b/cpu/nrf51822/cpu.c
index 8707095364..ff85420a35 100644
--- a/cpu/nrf51822/cpu.c
+++ b/cpu/nrf51822/cpu.c
@@ -18,6 +18,7 @@
  */
 
 #include "cpu.h"
+#include "periph_conf.h"
 
 /**
  * @brief Initialize the CPU, set IRQ priorities
@@ -26,4 +27,17 @@ void cpu_init(void)
 {
     /* set pendSV interrupt to lowest possible priority */
     NVIC_SetPriority(PendSV_IRQn, 0xff);
+
+    /* set the correct clock source for HFCLK */
+#if CLOCK_CRYSTAL == 32
+    NRF_CLOCK->XTALFREQ = CLOCK_XTALFREQ_XTALFREQ_32MHz;
+    NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
+    NRF_CLOCK->TASKS_HFCLKSTART = 1;
+    while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
+#elif CLOCK_CRYSTAL == 16
+    NRF_CLOCK->XTALFREQ = CLOCK_XTALFREQ_XTALFREQ_16MHz;
+    NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
+    NRF_CLOCK->TASKS_HFCLKSTART = 1;
+    while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
+#endif
 }