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 e2868aa10f..1d127a7d36 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 bfe53b7b43..1b800139ab 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 259d8fadf3..32b85d7da0 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
  * @{