diff --git a/src/common/conversions.c b/src/common/conversions.c
index 04156bc6..1d24e25e 100644
--- a/src/common/conversions.c
+++ b/src/common/conversions.c
@@ -50,12 +50,44 @@ time_t timegm (struct tm *tm)
 
 #ifdef _WIN32
 
-time_t
-timegm(struct tm* tm_time)
+#ifndef _MSC_VER
+/* Algorithm: http://howardhinnant.github.io/date_algorithms.html */
+static int 
+days_from_civil(int y, int m, int d)
 {
-    return mktime(tm_time) - _timezone;
+	y -= m <= 2;
+	int era = y / 400;
+	int yoe = y - era * 400;                                   /* [0, 399] */
+	int doy = (153 * (m + (m > 2 ? -3 : 9)) + 2) / 5 + d - 1;  /* [0, 365] */
+	int doe = yoe * 365 + yoe / 4 - yoe / 100 + doy;           /* [0, 146096] */
+	return era * 146097 + doe - 719468;
 }
 
+/* from https://stackoverflow.com/questions/16647819/timegm-cross-platform */
+time_t 
+timegm(tm const* t) /* does not modify broken-down time */
+{
+	int year = t->tm_year + 1900;
+	int month = t->tm_mon;          /* 0-11 */
+	if (month > 11)
+	{
+		year += month / 12;
+		month %= 12;
+	}
+	else if (month < 0)
+	{
+		int years_diff = (11 - month) / 12;
+		year -= years_diff;
+		month += 12 * years_diff;
+	}
+	int days_since_1970 = days_from_civil(year, month + 1, t->tm_mday);
+
+	return 60 * (60 * (24L * days_since_1970 + t->tm_hour) + t->tm_min) + t->tm_sec;
+}
+#else
+#define timegm _mkgmtime
+#endif
+
 #if defined(__MINGW32__)
 
 static inline // assuming gmtime is thread safe in windows!
@@ -169,7 +201,7 @@ getSecondsOffset(const char* offsetString)
 uint64_t
 Conversions_generalizedTimeToMsTime(const char* gtString)
 {
-    int gtStringLen = strlen(gtString);
+    int gtStringLen = (int) strlen(gtString);
 
     if (gtStringLen < 14) return -1;