diff --git a/lib/icinga/legacytimeperiod.cpp b/lib/icinga/legacytimeperiod.cpp
index 039fedc78..560a588ec 100644
--- a/lib/icinga/legacytimeperiod.cpp
+++ b/lib/icinga/legacytimeperiod.cpp
@@ -181,6 +181,9 @@ void LegacyTimePeriod::ParseTimeSpec(const String& timespec, tm *begin, tm *end,
 			if (mday < 0) {
 				boost::gregorian::date d(GetEndOfMonthDay(reference->tm_year + 1900, mon + 1)); //TODO: Refactor this mess into full Boost.DateTime
 
+				//Depending on the number, we need to substract specific days (counting starts at 0).
+				d = d - boost::gregorian::days(mday * -1 - 1);
+
 				*begin = boost::gregorian::to_tm(d);
 				begin->tm_hour = 0;
 				begin->tm_min = 0;
@@ -200,6 +203,9 @@ void LegacyTimePeriod::ParseTimeSpec(const String& timespec, tm *begin, tm *end,
 			if (mday < 0) {
 				boost::gregorian::date d(GetEndOfMonthDay(reference->tm_year + 1900, mon + 1)); //TODO: Refactor this mess into full Boost.DateTime
 
+				//Depending on the number, we need to substract specific days (counting starts at 0).
+				d = d - boost::gregorian::days(mday * -1 - 1);
+
 				// End date is one day in the future, starting 00:00:00
 				d = d + boost::gregorian::days(1);
 
diff --git a/test/icinga-legacytimeperiod.cpp b/test/icinga-legacytimeperiod.cpp
index f27a56477..c7eb51b06 100644
--- a/test/icinga-legacytimeperiod.cpp
+++ b/test/icinga-legacytimeperiod.cpp
@@ -158,6 +158,26 @@ BOOST_AUTO_TEST_CASE(simple)
 	BOOST_CHECK_EQUAL(begin, expectedBegin);
 	BOOST_CHECK_EQUAL(end, expectedEnd);
 
+	//-----------------------------------------------------
+	// Third last day of the month
+	timestamp = "day -3";
+	tm_ref.tm_year = 2019 - 1900;
+	tm_ref.tm_mon = 7 - 1;
+
+	expectedBegin = boost::posix_time::ptime(boost::gregorian::date(2019, 7, 29), boost::posix_time::time_duration(0, 0, 0));
+
+	expectedEnd = boost::posix_time::ptime(boost::gregorian::date(2019, 7, 30), boost::posix_time::time_duration(0, 0, 0));
+
+	// Run Tests
+	LegacyTimePeriod::ParseTimeSpec(timestamp, &tm_beg, &tm_end, &tm_ref);
+
+	// Compare times
+	begin = boost::posix_time::ptime_from_tm(tm_beg);
+	end = boost::posix_time::ptime_from_tm(tm_end);
+
+	BOOST_CHECK_EQUAL(begin, expectedBegin);
+	BOOST_CHECK_EQUAL(end, expectedEnd);
+
 	//-----------------------------------------------------
 	// Leap year with the last day of the month
 	timestamp = "day -1";