diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 907105571..a7391d09a 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -850,7 +850,7 @@ ngx_http_upstream_cache(ngx_http_request_t *r, ngx_http_upstream_t *u)
 
         ngx_http_file_cache_create_key(r);
 
-        if (r->cache->header_start + 256 >= u->conf->buffer_size) {
+        if (r->cache->header_start + 256 > u->conf->buffer_size) {
             ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                           "%V_buffer_size %uz is not enough for cache key, "
                           "it should be increased to at least %uz",