diff --git a/honoka/src/honoka_imengine.h b/honoka/src/honoka_imengine.h
index 3f90832..a2cc2ad 100644
--- a/honoka/src/honoka_imengine.h
+++ b/honoka/src/honoka_imengine.h
@@ -56,6 +56,8 @@
 using namespace scim;
 using namespace std;
 
+class ACPredictor;
+
 class HonokaFactory : public IMEngineFactoryBase
 {
 protected: