diff --git a/boards/avsextrem/include/periph_conf.h b/boards/avsextrem/include/periph_conf.h
index a0851e9ddb..cacae833d5 100644
--- a/boards/avsextrem/include/periph_conf.h
+++ b/boards/avsextrem/include/periph_conf.h
@@ -29,6 +29,8 @@ extern "C" {
  * @name    Clock configuration
  * @{
  */
+#define XTAL_HZ             (16000000U)         /* the board provides a 16 MHz XTAL */
+
 #define CLOCK_CORECLOCK     (72000000U)         /* this board runs with 72MHz */
 
 #define CLOCK_PCLK          (CLOCK_CORECLOCK)
diff --git a/boards/msba2/include/periph_conf.h b/boards/msba2/include/periph_conf.h
index b0a9e66692..ed9d084488 100644
--- a/boards/msba2/include/periph_conf.h
+++ b/boards/msba2/include/periph_conf.h
@@ -29,6 +29,8 @@ extern "C" {
  * @name    Clock configuration
  * @{
  */
+#define XTAL_HZ             (16000000U)         /* the board provides a 16 MHz XTAL */
+
 #define CLOCK_CORECLOCK     (72000000U)         /* the msba2 runs with 72MHz */
 
 #define CLOCK_PCLK          (CLOCK_CORECLOCK)