diff --git a/libavformat/wtv.c b/libavformat/wtv.c
index 07549b2cc5..83f1bc17eb 100644
--- a/libavformat/wtv.c
+++ b/libavformat/wtv.c
@@ -443,7 +443,11 @@ static int read_probe(AVProbeData *p)
 static void filetime_to_iso8601(char *buf, int buf_size, int64_t value)
 {
     time_t t = (value / 10000000LL) - 11644473600LL;
-    strftime(buf, buf_size, "%Y-%m-%d %H:%M:%S", gmtime(&t));
+    struct tm *tm = gmtime(&t);
+    if (tm)
+        strftime(buf, buf_size, "%Y-%m-%d %H:%M:%S", gmtime(&t));
+    else
+        buf[0] = '\0';
 }
 
 /**
@@ -452,7 +456,11 @@ static void filetime_to_iso8601(char *buf, int buf_size, int64_t value)
 static void crazytime_to_iso8601(char *buf, int buf_size, int64_t value)
 {
     time_t t = (value / 10000000LL) - 719162LL*86400LL;
-    strftime(buf, buf_size, "%Y-%m-%d %H:%M:%S", gmtime(&t));
+    struct tm *tm = gmtime(&t);
+    if (tm)
+        strftime(buf, buf_size, "%Y-%m-%d %H:%M:%S", gmtime(&t));
+    else
+        buf[0] = '\0';
 }
 
 /**
@@ -461,7 +469,11 @@ static void crazytime_to_iso8601(char *buf, int buf_size, int64_t value)
 static void oledate_to_iso8601(char *buf, int buf_size, int64_t value)
 {
     time_t t = 631112400LL + 86400*av_int2double(value);
-    strftime(buf, buf_size, "%Y-%m-%d %H:%M:%S", gmtime(&t));
+    struct tm *tm = gmtime(&t);
+    if (tm)
+        strftime(buf, buf_size, "%Y-%m-%d %H:%M:%S", gmtime(&t));
+    else
+        buf[0] = '\0';
 }
 
 static void get_attachment(AVFormatContext *s, AVIOContext *pb, int length)