diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index 6feb6cc..257c406 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -1647,6 +1647,12 @@
     ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                    "http large header copy: %uz", r->header_in->pos - old);
 
+    if (r->header_in->pos - old > b->end - b->start) {
+        ngx_log_error(NGX_LOG_ALERT, r->connection->log, 0,
+                      "too large header to copy");
+        return NGX_ERROR;
+    }
+
     new = b->start;
 
     ngx_memcpy(new, old, r->header_in->pos - old);