diff --git a/include/mod_auth.h b/include/mod_auth.h
index 867c0f8dab..16cc50306e 100644
--- a/include/mod_auth.h
+++ b/include/mod_auth.h
@@ -30,6 +30,7 @@
 #include "apr_optional.h"
 
 #include "httpd.h"
+#include "http_config.h"
 
 #ifdef __cplusplus
 extern "C" {