diff --git a/roofit/histfactory/src/HistoToWorkspaceFactoryFast.cxx b/roofit/histfactory/src/HistoToWorkspaceFactoryFast.cxx
index c24a012919f96..e146d1aaf616f 100644
--- a/roofit/histfactory/src/HistoToWorkspaceFactoryFast.cxx
+++ b/roofit/histfactory/src/HistoToWorkspaceFactoryFast.cxx
@@ -832,6 +832,7 @@ RooArgList HistoToWorkspaceFactoryFast::createObservables(const TH1 *hist, RooWo
       constraintTermNames.push_back("lumiConstraint");
     } else {
       proto.var("Lumi")->setConstant();
+      proto.defineSet("globalObservables",RooArgSet()); // create empty set as is assumed it exists later
     }
     //proto.factory("SigXsecOverSM[1.,0.5,1..8]");
     ///////////////////////////////////