diff --git a/src/client/client.cpp b/src/client/client.cpp
index 935a82653..0a1fc73d1 100644
--- a/src/client/client.cpp
+++ b/src/client/client.cpp
@@ -1810,11 +1810,10 @@ void Client::makeScreenshot()
 	if (!raw_image)
 		return;
 
-	time_t t = time(NULL);
-	struct tm *tm = localtime(&t);
+	const struct tm tm = mt_localtime();
 
 	char timetstamp_c[64];
-	strftime(timetstamp_c, sizeof(timetstamp_c), "%Y%m%d_%H%M%S", tm);
+	strftime(timetstamp_c, sizeof(timetstamp_c), "%Y%m%d_%H%M%S", &tm);
 
 	std::string screenshot_dir;
 
diff --git a/src/gettime.h b/src/gettime.h
index 66efef1d7..772ff9b50 100644
--- a/src/gettime.h
+++ b/src/gettime.h
@@ -21,6 +21,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #include <ctime>
 #include <string>
+#include <mutex>
 
 enum TimePrecision
 {
@@ -30,13 +31,34 @@ enum TimePrecision
 	PRECISION_NANO
 };
 
+inline struct tm mt_localtime()
+{
+	// initialize the time zone on first invocation
+	static std::once_flag tz_init;
+	std::call_once(tz_init, [] {
+#ifdef _WIN32
+		_tzset();
+#else
+		tzset();
+#endif
+		});
+
+	struct tm ret;
+	time_t t = time(NULL);
+	// TODO we should check if the function returns NULL, which would mean error
+#ifdef _WIN32
+	localtime_s(&ret, &t);
+#else
+	localtime_r(&t, &ret);
+#endif
+	return ret;
+}
+
+
 inline std::string getTimestamp()
 {
-	time_t t = time(NULL);
-	// This is not really thread-safe but it won't break anything
-	// except its own output, so just go with it.
-	struct tm *tm = localtime(&t);
+	const struct tm tm = mt_localtime();
 	char cs[20]; // YYYY-MM-DD HH:MM:SS + '\0'
-	strftime(cs, 20, "%Y-%m-%d %H:%M:%S", tm);
+	strftime(cs, 20, "%Y-%m-%d %H:%M:%S", &tm);
 	return cs;
 }