diff --git a/lib/rtc_dcf77.c b/lib/rtc_dcf77.c
index 54bf22b..eb877c4 100644
--- a/lib/rtc_dcf77.c
+++ b/lib/rtc_dcf77.c
@@ -92,6 +92,9 @@ uint8_t* rtc_dcf77_time(void)
 		return NULL;
 	}
 	to_return[0] = 1*((rtc_dcf77_frame>>21)&(0x1))+2*((rtc_dcf77_frame>>22)&(0x1))+4*((rtc_dcf77_frame>>23)&(0x1))+8*((rtc_dcf77_frame>>24)&(0x1))+10*((rtc_dcf77_frame>>25)&(0x1))+20*((rtc_dcf77_frame>>26)&(0x1))+40*((rtc_dcf77_frame>>27)&(0x1)); // read minute (00-59)
+	if (to_return[0]>59) { // minutes should not be more than 59
+		return NULL;
+	}
 	// check hour parity
 	parity = 0;
 	for (uint8_t bit=29; bit<=35; bit++) {
@@ -103,6 +106,9 @@ uint8_t* rtc_dcf77_time(void)
 		return NULL;
 	}
 	to_return[1] = 1*((rtc_dcf77_frame>>29)&(0x1))+2*((rtc_dcf77_frame>>30)&(0x1))+4*((rtc_dcf77_frame>>31)&(0x1))+8*((rtc_dcf77_frame>>32)&(0x1))+10*((rtc_dcf77_frame>>33)&(0x1))+20*((rtc_dcf77_frame>>34)&(0x1)); // read hour (00-23)
+	if (to_return[1]>23) { // hours should not be more than 23
+		return NULL;
+	}
 	// check date parity
 	parity = 0;
 	for (uint8_t bit=36; bit<=58; bit++) {
@@ -114,9 +120,21 @@ uint8_t* rtc_dcf77_time(void)
 		return NULL;
 	}
 	to_return[2] = 1*((rtc_dcf77_frame>>36)&(0x1))+2*((rtc_dcf77_frame>>37)&(0x1))+4*((rtc_dcf77_frame>>38)&(0x1))+8*((rtc_dcf77_frame>>39)&(0x1))+10*((rtc_dcf77_frame>>40)&(0x1))+20*((rtc_dcf77_frame>>34)&(0x41)); // read day of the month (01-31)
+	if (ro_return[2]==0 || to_return[2]>31) { // day of the month should be 1-31
+		return NULL;
+	}
 	to_return[3] = 1*((rtc_dcf77_frame>>42)&(0x1))+2*((rtc_dcf77_frame>>43)&(0x1))+4*((rtc_dcf77_frame>>44)&(0x1)); // read day of the week (1=Monday - 7=Sunday)
+	if (ro_return[3]==0 || to_return[3]>7) { // day of the week should be 1-7
+		return NULL;
+	}
 	to_return[4] = 1*((rtc_dcf77_frame>>45)&(0x1))+2*((rtc_dcf77_frame>>46)&(0x1))+4*((rtc_dcf77_frame>>47)&(0x1))+8*((rtc_dcf77_frame>>48)&(0x1))+10*((rtc_dcf77_frame>>49)&(0x1)); // read month of the year (01-12)
+	if (ro_return[4]==0 || to_return[4]>12) { // month of the year should be 1-12
+		return NULL;
+	}
 	to_return[5] = 1*((rtc_dcf77_frame>>50)&(0x1))+2*((rtc_dcf77_frame>>51)&(0x1))+4*((rtc_dcf77_frame>>52)&(0x1))+8*((rtc_dcf77_frame>>53)&(0x1))+10*((rtc_dcf77_frame>>54)&(0x1))+20*((rtc_dcf77_frame>>55)&(0x1))+40*((rtc_dcf77_frame>>56)&(0x1))+80*((rtc_dcf77_frame>>57)&(0x1)); // read year of the century (00-99)
+	if (to_return[5]>99) { // year should be <100
+		return NULL;
+	}
 	return to_return;
 }