diff --git a/boards/common/iotlab/include/periph_conf_common.h b/boards/common/iotlab/include/periph_conf_common.h
index 51af7f58d2..7cce184d36 100644
--- a/boards/common/iotlab/include/periph_conf_common.h
+++ b/boards/common/iotlab/include/periph_conf_common.h
@@ -135,7 +135,7 @@ static const uart_conf_t uart_config[] = {
  * @{
  */
 #ifndef RTT_FREQUENCY
-#define RTT_FREQUENCY       (1)             /* in Hz */
+#define RTT_FREQUENCY       (RTT_MAX_FREQUENCY)     /* in Hz */
 #endif
 /** @} */
 
diff --git a/boards/fox/include/periph_conf.h b/boards/fox/include/periph_conf.h
index 1dcb09590c..52cc9a8e79 100644
--- a/boards/fox/include/periph_conf.h
+++ b/boards/fox/include/periph_conf.h
@@ -117,7 +117,7 @@ static const spi_conf_t spi_config[] = {
  * @{
  */
 #ifndef RTT_FREQUENCY
-#define RTT_FREQUENCY       (1)             /* in Hz */
+#define RTT_FREQUENCY       (RTT_MAX_FREQUENCY)     /* in Hz */
 #endif
 /** @} */