diff --git a/src/core/ngx_times.c b/src/core/ngx_times.c
index be289dd14..551e10258 100644
--- a/src/core/ngx_times.c
+++ b/src/core/ngx_times.c
@@ -87,7 +87,7 @@ ngx_time_update(time_t sec, ngx_uint_t msec)
         return;
     }
 
-    if (slot == NGX_TIME_SLOTS) {
+    if (slot == NGX_TIME_SLOTS - 1) {
         slot = 0;
     } else {
         slot++;