diff --git a/cpu/cortexm_common/include/cpu_conf_common.h b/cpu/cortexm_common/include/cpu_conf_common.h
index 8d2d17744e14ca27cf34993a9f430fca2348b130..513d53da09557ec942e02006cc295880a0f1765f 100644
--- a/cpu/cortexm_common/include/cpu_conf_common.h
+++ b/cpu/cortexm_common/include/cpu_conf_common.h
@@ -57,6 +57,17 @@ extern "C" {
 #endif
 /** @} */
 
+/**
+ * @brief   Select fastest bitarithm_lsb implementation
+ * @{
+ */
+#ifdef __ARM_FEATURE_CLZ
+#define BITARITHM_LSB_BUILTIN
+#else
+#define BITARITHM_LSB_LOOKUP
+#endif
+/** @} */
+
 #ifdef __cplusplus
 }
 #endif