Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -459,10 +459,24 @@
 	AC_DEFINE(HAVE_GMTIME_R, 1, [Whether we have gmtime_r])
 ])
 AC_CHECK_FUNC(localtime_r, [
 	AC_DEFINE(HAVE_LOCALTIME_R, 1, [Whether we have localtime_r])
 ])
+
+AC_MSG_CHECKING(for tm_gmtoff in struct tm)
+AC_TRY_COMPILE([
+	#define _GNU_SOURCE
+	#include <time.h>
+], [
+	struct tm tm;
+	tm.tm_gmtoff = 0;
+], [
+	AC_DEFINE(STRUCT_TM_HAS_TM_GMTOFF, 1, [Whether struct tm has tm_gmtoff])
+	AC_MSG_RESULT(yes)
+], [
+	AC_MSG_RESULT(no)
+])
 
 AC_CHECK_FUNC(kqueue, [
 	AC_DEFINE(HAVE_KQUEUE, 1, [Whether we have kqueue])
 	AC_SUBST(OFSTREAMOBSERVER_KQUEUE_M, "OFStreamObserver_kqueue.m")
 ])

Index: src/OFDate.m
==================================================================
--- src/OFDate.m
+++ src/OFDate.m
@@ -131,10 +131,25 @@
 		@throw [OFOutOfRangeException exceptionWithClass: isa];	\
 									\
 	return tm->field;
 # endif
 #endif
+
+static int month_to_day_of_year[12] = {
+	31,
+	31 + 28,
+	31 + 28 + 31,
+	31 + 28 + 31 + 30,
+	31 + 28 + 31 + 30 + 31,
+	31 + 28 + 31 + 30 + 31 + 30,
+	31 + 28 + 31 + 30 + 31 + 30 + 31,
+	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31,
+	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30,
+	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31,
+	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30,
+	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + 31
+};
 
 @implementation OFDate
 #if (!defined(HAVE_GMTIME_R) || !defined(HAVE_LOCALTIME_R)) && \
     defined(OF_THREADS)
 + (void)initialize
@@ -232,19 +247,33 @@
 		if (strptime([string UTF8String], [format UTF8String],
 		    &tm) == NULL)
 			@throw [OFInvalidFormatException
 			    exceptionWithClass: isa];
 
-		if (tm.tm_gmtoff)
+#ifdef STRUCT_TM_HAS_TM_GMTOFF
+		if (tm.tm_gmtoff != 0)
 			@throw [OFInvalidFormatException
 			    exceptionWithClass: isa];
+#endif
 
-		if ((seconds = mktime(&tm)) == -1)
+		/* Years */
+		seconds = (tm.tm_year - 70) * 31536000;
+		/* Leap years */
+		seconds += ((tm.tm_year / 4) - 17) * 86400;
+		/* Months */
+		if (tm.tm_mon < 0 || tm.tm_mon > 12)
 			@throw [OFInvalidFormatException
 			    exceptionWithClass: isa];
-
-		seconds += tm.tm_gmtoff;
+		seconds += month_to_day_of_year[tm.tm_mon - 1] * 86400;
+		/* Days */
+		seconds += (tm.tm_mday - 1) * 86400;
+		/* Hours */
+		seconds += tm.tm_hour * 3600;
+		/* Minutes */
+		seconds += tm.tm_min * 60;
+		/* Seconds */
+		seconds += tm.tm_sec;
 	} @catch (id e) {
 		[self release];
 		@throw e;
 	}