=== modified file 'src/SysCalc.cc'
--- old/src/SysCalc.cc	2015-10-21 21:12:44 +0000
+++ new/src/SysCalc.cc	2016-01-22 11:27:53 +0000
@@ -652,20 +652,20 @@
   int max = pdg.size()-1;
   double maxq = fact*q[max];
   int maxpdg = beam*pdg[max];
-  if(abs(maxpdg) == 21) maxpdg = 0;
+  if(abs(maxpdg) >= 21) maxpdg = abs(maxpdg)-21;
   maxpdg += 6;
-  vector<double> pdfs = xfx(pdfnum, x[max], maxq);
+  vector<double> pdfs = xfxphoton(pdfnum, x[max], maxq);
   weight *= pdfs[maxpdg]/x[max];
   int pdgnow;
   for(int i=0; i < max; i++){
-    pdfs = xfx(pdfnum, x[i], min(q[i], maxq));
+    pdfs = xfxphoton(pdfnum, x[i], min(q[i], maxq));
     pdgnow = beam*pdg[i];
-    if(abs(pdgnow) == 21) pdgnow = 0;
+    if(abs(pdgnow) >= 21) pdgnow = abs(pdgnow)-21;
     pdgnow += 6;
     weight *= pdfs[pdgnow]/x[i];
-    pdfs = xfx(pdfnum, x[i+1], min(q[i], maxq));
+    pdfs = xfxphoton(pdfnum, x[i+1], min(q[i], maxq));
     pdgnow = beam*pdg[i+1];
-    if(abs(pdgnow) == 21) pdgnow = 0;
+    if(abs(pdgnow) >= 21) pdgnow = abs(maxpdg)-21;
     pdgnow += 6;
     weight /= (pdfs[pdgnow]/x[i+1]);
   }