diff --git a/include/libwebsockets/lws-ws-ext.h b/include/libwebsockets/lws-ws-ext.h
index 10c7a644d..2d7f22b8b 100644
--- a/include/libwebsockets/lws-ws-ext.h
+++ b/include/libwebsockets/lws-ws-ext.h
@@ -184,7 +184,7 @@ lws_ext_parse_options(const struct lws_extension *ext, struct lws *wsi,
  *
  * Built-in callback implementing RFC7692 permessage-deflate
  */
-LWS_EXTERN int
+LWS_VISIBLE LWS_EXTERN int
 lws_extension_callback_pm_deflate(struct lws_context *context,
 				  const struct lws_extension *ext,
 				  struct lws *wsi,