diff --git a/boards/ek-lm4f120xl/include/periph_conf.h b/boards/ek-lm4f120xl/include/periph_conf.h
index 69d0d9c5b45085e69e2a084098e278e64f2abe76..e2de1321cb3838f70b3ebd49b6edef1cf526d95e 100644
--- a/boards/ek-lm4f120xl/include/periph_conf.h
+++ b/boards/ek-lm4f120xl/include/periph_conf.h
@@ -27,7 +27,6 @@ extern "C" {
  * @name Define the nominal CPU core clock in this board
  * @{
  */
-#define F_CPU                           1000000
 #define CLK80                           1
 #define CLK50                           2
 #define CLK40                           3
diff --git a/boards/mulle/include/periph_conf.h b/boards/mulle/include/periph_conf.h
index 11467b5abecee6573a1372e9964941b67b40d54c..09628b626df271e72eae52cfb7d1b7a96976573d 100644
--- a/boards/mulle/include/periph_conf.h
+++ b/boards/mulle/include/periph_conf.h
@@ -50,10 +50,6 @@ extern "C"
 #define CPU_INT_FAST_CLK_HZ             4000000u
 /** Default System clock value */
 #define DEFAULT_SYSTEM_CLOCK            (CPU_XTAL32k_CLK_HZ * 2929u)
-
-/** @todo Investigate the side effects of making F_CPU run-time variable */
-#define F_CPU DEFAULT_SYSTEM_CLOCK
-
 /** @} */
 
 /**