diff --git a/src/classes/PRunAsymmetryRRF.cpp b/src/classes/PRunAsymmetryRRF.cpp
index 59ef55706..02f22a442 100644
--- a/src/classes/PRunAsymmetryRRF.cpp
+++ b/src/classes/PRunAsymmetryRRF.cpp
@@ -918,16 +918,28 @@ Bool_t PRunAsymmetryRRF::PrepareFitData()
     lgb_offset = fGoodBins[3]-static_cast<Int_t>(fT0s[1])+fgbOffset;
 
   Int_t fgb = static_cast<Int_t>(fT0s[0])+fgbOffset;
+  if (fgb < 0)
+    fgb=0;
   Int_t lgb = fgb + lgb_offset;
+  if (lgb > fForward.size())
+    lgb = fForward.size();
+  if (lgb > fBackward.size())
+    lgb = fBackward.size();
   Int_t dt0 = static_cast<Int_t>(fT0s[0])-static_cast<Int_t>(fT0s[1]);
 
   PDoubleVector asym;
   PDoubleVector asymErr;
   Double_t asymVal, asymValErr;
   Double_t ff, bb, eff, ebb;
+  Int_t idx=0;
   for (Int_t i=fgb; i<lgb; i++) {
     ff = fForward[i];
-    bb = fBackward[i-dt0];
+    idx = i-dt0;
+    if (idx < 0)
+      idx = 0;
+    if (idx >= fBackward.size())
+      idx = fBackward.size()-1;
+    bb = fBackward[idx];
     if (ff+bb != 0.0)
       asymVal = (ff-bb)/(ff+bb);
     else