Index: src/celastro/date.cpp
--- src/celastro/date.cpp.orig
+++ src/celastro/date.cpp
@@ -201,7 +201,7 @@ Date::toString(const std::locale& loc, Format format) 
     cal_time.tm_sec = (int)seconds;
     cal_time.tm_wday = wday;
     cal_time.tm_gmtoff = utc_offset;
-#if defined(__APPLE__) || defined(__FreeBSD__)
+#if defined(__APPLE__) || defined(__FreeBSD__) || defined(__OpenBSD__)
     // tm_zone is a non-const string field on the Mac and FreeBSD (why?)
     cal_time.tm_zone = const_cast<char*>(tzname.c_str());
 #else
