diff --git a/include/kernel.h b/include/kernel.h
index 1828b016fb4..f77584ac367 100644
--- a/include/kernel.h
+++ b/include/kernel.h
@@ -237,6 +237,16 @@ extern void *k_thread_custom_data_get(void);
  *  kernel timing
  */
 
+#include <sys_clock.h>
+
+/* private internal time manipulation (users should never play with ticks) */
+
+static int64_t __ticks_to_ms(int64_t ticks)
+{
+	return (MSEC_PER_SEC * (uint64_t)ticks) / sys_clock_ticks_per_sec;
+}
+
+
 /* timeouts */
 
 struct _timeout;
diff --git a/include/legacy.h b/include/legacy.h
index d69963e1b1d..8a1b210e037 100644
--- a/include/legacy.h
+++ b/include/legacy.h
@@ -26,7 +26,6 @@
 #include <stdint.h>
 #include <errno.h>
 #include <limits.h>
-#include <sys_clock.h>
 
 /* nanokernel/microkernel execution context types */
 #define NANO_CTX_ISR (K_ISR)
@@ -60,8 +59,7 @@ typedef enum {
 
 static inline int32_t _ticks_to_ms(int32_t ticks)
 {
-	return (ticks == TICKS_UNLIMITED) ? K_FOREVER :
-		(MSEC_PER_SEC * (uint64_t)ticks) / sys_clock_ticks_per_sec;
+	return (ticks == TICKS_UNLIMITED) ? K_FOREVER : __ticks_to_ms(ticks);
 }
 
 static inline int _error_to_rc(int err)