diff --git a/firmware/common/timefuncs.c b/firmware/common/timefuncs.c
index f5097c8e52..e59534eeba 100644
--- a/firmware/common/timefuncs.c
+++ b/firmware/common/timefuncs.c
@@ -196,7 +196,7 @@ time_t mktime(struct tm *t)
 
 int day_of_week(int m, int d, int y)
 {
-        char mo[12] = { 0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4 };
+        static const char mo[] = { 0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4 };
 
         if(m == 0 || m == 1) y--;
         return (d + mo[m] + y + y/4 - y/100 + y/400) % 7;
@@ -204,31 +204,25 @@ int day_of_week(int m, int d, int y)
 
 void yearday_to_daymonth(int yd, int y, int *d, int *m)
 {
-    short t[12] = { 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 };
-    int i;
+    static const char tnl[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
+    static const char tl[] = { 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
+    const char *t;
+    int i=0;
 
     if((y%4 == 0 && y%100 != 0) || y%400 == 0)
     {
-        for(i=1;i<12;i++)
-            t[i]++;
-    }
-
-    yd++;
-    if(yd <= 31)
-    {
-        *d = yd;
-        *m = 0;
+        t=tl;
     }
     else
     {
-        for(i=1;i<12;i++)
-        {
-            if(yd <= t[i])
-            {
-                *d = yd - t[i-1];
-                *m = i;
-                break;
-            }
-        }
+        t=tnl;
     }
+
+    while(yd >= t[i] && i<12)
+    {
+        yd-=t[i];
+        i++;
+    }
+    *d = yd+1;
+    *m = i;
 }