diff --git a/src/core/ngx_core.h b/src/core/ngx_core.h
index 1b7549914..24ffc3d9e 100644
--- a/src/core/ngx_core.h
+++ b/src/core/ngx_core.h
@@ -72,6 +72,7 @@ typedef void (*ngx_connection_handler_pt)(ngx_connection_t *c);
 #endif
 #include <ngx_process_cycle.h>
 #include <ngx_conf_file.h>
+#include <ngx_resolver.h>
 #include <ngx_open_file_cache.h>
 #include <ngx_os.h>
 #include <ngx_connection.h>