diff --git a/sys/include/timex.h b/sys/include/timex.h
index f022ad362a..2c4506cce3 100644
--- a/sys/include/timex.h
+++ b/sys/include/timex.h
@@ -63,6 +63,11 @@ extern "C" {
  */
 #define NS_PER_US  (1000U)
 
+/**
+ * @brief The number of nanoseconds per second
+ */
+#define NS_PER_SEC  (1000000000U)
+
 /**
  * @brief The maximum length of the string representation of a timex timestamp
  */