diff --git a/Generators/GenInterfaces/GenInterfaces/IHiggsTruthCategoryTool.h b/Generators/GenInterfaces/GenInterfaces/IHiggsTruthCategoryTool.h
index 0c9b95d9c77bc5d35b52dc38f03699d4ec6342ca..c4ddab167f6898e691915db6018bb662ac9333a2 100644
--- a/Generators/GenInterfaces/GenInterfaces/IHiggsTruthCategoryTool.h
+++ b/Generators/GenInterfaces/GenInterfaces/IHiggsTruthCategoryTool.h
@@ -15,7 +15,7 @@
 #include "HepMC/GenEvent.h"
 
 namespace HTXS {
-  class HiggsClassification;
+  struct HiggsClassification;
 }
 
 class IHiggsTruthCategoryTool : public virtual asg::IAsgTool {