diff --git a/cfg/vnstat.conf b/cfg/vnstat.conf
index 343ce71d..706bd314 100644
--- a/cfg/vnstat.conf
+++ b/cfg/vnstat.conf
@@ -15,9 +15,9 @@ MonthRotate 1
 
 # date output formats for -d, -m, -t and -w
 # see 'man date' for control codes
-DayFormat    "%x"
-MonthFormat  "%b '%y"
-TopFormat    "%x"
+DayFormat    "%Y-%m-%d"
+MonthFormat  "%Y-%m"
+TopFormat    "%Y-%m-%d"
 
 # characters used for visuals
 RXCharacter       "%"
@@ -152,7 +152,7 @@ PidFile "/var/run/vnstat/vnstat.pid"
 ##
 
 # title timestamp format
-HeaderFormat "%x %H:%M"
+HeaderFormat "%Y-%m-%d %H:%M"
 
 # show hours with rate (1 = enabled, 0 = disabled)
 HourlyRate 1
diff --git a/src/common.h b/src/common.h
index 4f5f1fca..3ecd019c 100644
--- a/src/common.h
+++ b/src/common.h
@@ -74,11 +74,11 @@ and most can be changed later from the config file.
 #define MONTHROTATE 1
 
 /* date output formats for -d, -m, -t and image header*/
-/* see 'man date' for control codes       <1.8 values */
-#define DFORMAT "%x"                    /* "%d.%m." */
-#define MFORMAT "%b '%y"                /* "%b '%y" */
-#define TFORMAT "%x"                    /* "%d.%m.%y" */
-#define HFORMAT "%x %H:%M"              /* "%d.%m.%Y %H:%M" */
+/* see 'man date' for control codes      1.x values     <1.8 values */
+#define DFORMAT "%Y-%m-%d"             /* "%x"         "%d.%m." */
+#define MFORMAT "%Y-%m"                /* "%b '%y"     "%b '%y" */
+#define TFORMAT "%Y-%m-%d"             /* "%x"         "%d.%m.%y" */
+#define HFORMAT "%Y-%m-%d %H:%M"       /* "%x %H:%M"   "%d.%m.%Y %H:%M" */
 
 /* characters used for visuals */
 #define RXCHAR "%"