diff --git a/src/core/ngx_times.c b/src/core/ngx_times.c
index 16788c98c..d7ef77ef5 100644
--- a/src/core/ngx_times.c
+++ b/src/core/ngx_times.c
@@ -360,7 +360,7 @@ ngx_gmtime(time_t t, ngx_tm_t *tp)
      */
 
     /* days since March 1, 1 BC */
-    days = days - (31 + 28) + 719527;
+    days = days + 719527 - (31 + 28);
 
     /*
      * The "days" should be adjusted to 1 only, however, some March 1st's go
diff --git a/src/os/unix/ngx_time.c b/src/os/unix/ngx_time.c
index c97bae2ed..386b073eb 100644
--- a/src/os/unix/ngx_time.c
+++ b/src/os/unix/ngx_time.c
@@ -46,6 +46,9 @@ ngx_timezone_update(void)
     s = time(NULL);
 
     t = localtime(&s);
+    if (t == NULL) {
+        return;
+    }
 
     strftime(buf, 4, "%H", t);
 
@@ -57,12 +60,20 @@ void
 ngx_localtime(time_t s, ngx_tm_t *tm)
 {
 #if (NGX_HAVE_LOCALTIME_R)
-    (void) localtime_r(&s, tm);
+    if (localtime_r(&s, tm) == NULL) {
+        ngx_memzero(tm, sizeof(struct tm));
+        return;
+    }
 
 #else
     ngx_tm_t  *t;
 
     t = localtime(&s);
+    if (t == NULL) {
+        ngx_memzero(tm, sizeof(struct tm));
+        return;
+    }
+
     *tm = *t;
 
 #endif
@@ -76,12 +87,20 @@ void
 ngx_libc_localtime(time_t s, struct tm *tm)
 {
 #if (NGX_HAVE_LOCALTIME_R)
-    (void) localtime_r(&s, tm);
+    if (localtime_r(&s, tm) == NULL) {
+        ngx_memzero(tm, sizeof(struct tm));
+        return;
+    }
 
 #else
     struct tm  *t;
 
     t = localtime(&s);
+    if (t == NULL) {
+        ngx_memzero(tm, sizeof(struct tm));
+        return;
+    }
+
     *tm = *t;
 
 #endif
@@ -92,12 +111,20 @@ void
 ngx_libc_gmtime(time_t s, struct tm *tm)
 {
 #if (NGX_HAVE_LOCALTIME_R)
-    (void) gmtime_r(&s, tm);
+    if (gmtime_r(&s, tm) == NULL) {
+        ngx_memzero(tm, sizeof(struct tm));
+        return;
+    }
 
 #else
     struct tm  *t;
 
     t = gmtime(&s);
+    if (t == NULL) {
+        ngx_memzero(tm, sizeof(struct tm));
+        return;
+    }
+
     *tm = *t;
 
 #endif
diff --git a/src/os/win32/ngx_time.c b/src/os/win32/ngx_time.c
index 79149b2c7..d578d31d0 100644
--- a/src/os/win32/ngx_time.c
+++ b/src/os/win32/ngx_time.c
@@ -44,6 +44,11 @@ ngx_libc_localtime(time_t s, struct tm *tm)
     struct tm  *t;
 
     t = localtime(&s);
+    if (t == NULL) {
+        ngx_memzero(tm, sizeof(struct tm));
+        return;
+    }
+
     *tm = *t;
 }
 
@@ -54,6 +59,11 @@ ngx_libc_gmtime(time_t s, struct tm *tm)
     struct tm  *t;
 
     t = gmtime(&s);
+    if (t == NULL) {
+        ngx_memzero(tm, sizeof(struct tm));
+        return;
+    }
+
     *tm = *t;
 }