diff --git a/sys/shell/cmds/rtc.c b/sys/shell/cmds/rtc.c
index eca0bbc4bf..bb5326767a 100644
--- a/sys/shell/cmds/rtc.c
+++ b/sys/shell/cmds/rtc.c
@@ -27,6 +27,7 @@
 
 #include "container.h"
 #include "periph/rtc.h"
+#include "rtc_utils.h"
 #include "shell.h"
 
 static void _alarm_handler(void *arg)
@@ -36,19 +37,6 @@ static void _alarm_handler(void *arg)
     puts("The alarm rang");
 }
 
-static int dow(int year, int month, int day)
-{
-    /* calculate the day of week using Tøndering's algorithm */
-    static int t[] = {0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4};
-    if (month < 1 || month > (int) ARRAY_SIZE(t)) {
-        /* This will be a wrong answer, but error handling is not this
-         * function's task (whereas memory safety is). */
-        return 7;
-    }
-    year -= month < 3;
-    return (year + year/4 - year/100 + year/400 + t[month-1] + day) % 7;
-}
-
 /** Read a ["YYYY-MM-DD", "hh:mm:ss"] formatted value from a string array.
  *
  * This performs no validation on the entered time -- that'd be trivial on some
@@ -58,7 +46,7 @@ static int dow(int year, int month, int day)
  *
  * Invalid inputs merely lead to out-of-range values inside the time struct.
  */
-static int _parse_time(char **argv, struct tm *time)
+static void _parse_time(char **argv, struct tm *time)
 {
     short i;
     char *end;
@@ -81,10 +69,9 @@ static int _parse_time(char **argv, struct tm *time)
     i = strtol(end + 1, &end, 10);
     time->tm_sec = i;
 
-    time->tm_wday = dow(time->tm_year + 1900, time->tm_mon + 1, time->tm_mday);
     time->tm_isdst = -1; /* undefined */
 
-    return 0;
+    rtc_tm_normalize(time);
 }
 
 static int _print_time(struct tm *time)
@@ -113,14 +100,14 @@ static int _rtc_setalarm(char **argv)
 {
     struct tm now;
 
-    if (_parse_time(argv, &now) == 0) {
-        if (rtc_set_alarm(&now, _alarm_handler, NULL) == -1) {
-            puts("rtc: error setting alarm");
-            return 1;
-        }
-        return 0;
+    _parse_time(argv, &now);
+
+    if (rtc_set_alarm(&now, _alarm_handler, NULL) < 0) {
+        puts("rtc: error setting alarm");
+        return 1;
     }
-    return 1;
+
+    return 0;
 }
 
 static int _rtc_gettime(void)
@@ -140,14 +127,14 @@ static int _rtc_settime(char **argv)
 {
     struct tm now;
 
-    if (_parse_time(argv, &now) == 0) {
-        if (rtc_set_time(&now) == -1) {
-            puts("rtc: error setting time");
-            return 1;
-        }
-        return 0;
+    _parse_time(argv, &now);
+
+    if (rtc_set_time(&now) < 0) {
+        puts("rtc: error setting time");
+        return 1;
     }
-    return 1;
+
+    return 0;
 }
 
 static int _rtc_usage(void)