diff --git a/dom/plugins/PluginInstanceParent.h b/dom/plugins/PluginInstanceParent.h
index 912644d15cde..c2c772456446 100644
--- a/dom/plugins/PluginInstanceParent.h
+++ b/dom/plugins/PluginInstanceParent.h
@@ -54,6 +54,7 @@ namespace plugins {
 
 class PBrowserStreamParent;
 class BrowserStreamParent;
+class PluginModuleParent;
 
 class PluginInstanceParent : public PPluginInstanceParent
 {