diff --git a/src/VerticalInterpPdf.cc b/src/VerticalInterpPdf.cc
index a3b8febca58..5acb21a77e0 100644
--- a/src/VerticalInterpPdf.cc
+++ b/src/VerticalInterpPdf.cc
@@ -12,6 +12,7 @@
 #include "RooRealConstant.h"
 #include "RooRealIntegral.h"
 #include "RooMsgService.h"
+#include "RooProdPdf.h"
 
 
 
@@ -52,6 +53,10 @@ VerticalInterpPdf::VerticalInterpPdf(const char *name, const char *title, const
       coutE(InputArguments) << "ERROR: VerticalInterpPdf::VerticalInterpPdf(" << GetName() << ") function  " << func->GetName() << " is not of type RooAbsReal" << std::endl;
       assert(0);
     }
+    if (!dynamic_cast<RooProdPdf*>(func)) {
+      coutE(InputArguments) << "ERROR: with the HZZ hack in place, VerticalInterpPdf can only take RooProdPdf pdfs"<<std::endl;
+      assert(0);
+    }
     _funcList.add(*func) ;
   }
   delete funcIter;
@@ -209,12 +214,28 @@ Int_t VerticalInterpPdf::getAnalyticalIntegralWN(RooArgSet& allVars, RooArgSet&
   // Create new cache element
   cache = new CacheElem ;
 
+  TIterator* analVarsIter = analVars.createIterator();
+  RooRealVar *zmass = (RooRealVar*)analVarsIter->Next(); 
+  RooRealVar *dbkg = (RooRealVar*)analVarsIter->Next(); 
+
   // Make list of function projection and normalization integrals 
   _funcIter->Reset() ;
-  RooAbsReal *func ;
+  /*RooAbsReal *func ;
   while((func=(RooAbsReal*)_funcIter->Next())) {
     RooAbsReal* funcInt = func->createIntegral(analVars) ;
-    cache->_funcIntList.addOwned(*funcInt) ;
+    cache->_funcIntList.addOwned(*funcInt) ;*/
+  RooProdPdf *func;
+  while((func=(RooProdPdf*)_funcIter->Next())){
+    int i = 0;
+    std::auto_ptr<TIterator> iter(func->pdfList().createIterator());
+    for (RooAbsArg *a = (RooAbsArg *) iter->Next(); a!=0; a=(RooAbsArg*) iter->Next()){
+      i++;
+      RooAbsPdf *cterm = dynamic_cast<RooAbsPdf*>(a);
+      RooAbsReal* funcInt;
+      if(i==1) funcInt = cterm->createIntegral(*zmass);
+      else funcInt=cterm->createIntegral(*dbkg);
+      cache->_funcIntList.addOwned(*funcInt);
+    }
     if (normSet && normSet->getSize()>0) {
       RooAbsReal* funcNorm = func->createIntegral(*normSet) ;
       cache->_funcNormList.addOwned(*funcNorm) ;
@@ -251,15 +272,18 @@ Double_t VerticalInterpPdf::analyticalIntegralWN(Int_t code, const RooArgSet* no
 
   TIterator* funcIntIter = cache->_funcIntList.createIterator() ;
   RooAbsReal *funcInt = (RooAbsReal *) funcIntIter->Next();
+  RooAbsReal *funcInt2d = (RooAbsReal *) funcIntIter->Next();
   Double_t central = funcInt->getVal();
-  value += central;
+  value += central*funcInt2d->getVal();
 
   _coefIter->Reset() ;
   while((coef=(RooAbsReal*)_coefIter->Next())) {
     Double_t coefVal = coef->getVal(normSet2) ;
     RooAbsReal * funcIntUp = (RooAbsReal*)funcIntIter->Next() ;
+   /*RooAbsReal * funcIntUp2d =*/ (RooAbsReal*)funcIntIter->Next() ;
     RooAbsReal * funcIntDn = (RooAbsReal*)funcIntIter->Next() ;
-    value += interpolate(coefVal, central, funcIntUp, funcIntDn);
+   /*RooAbsReal * funcIntUp2d =*/ (RooAbsReal*)funcIntIter->Next() ;
+    value += interpolate(coefVal, central, funcIntUp, funcIntDn)*funcInt2d->getVal();
   }
   
   delete funcIntIter ;