diff --git a/Detectors/ITSMFT/common/reconstruction/include/ITSMFTReconstruction/PixelData.h b/Detectors/ITSMFT/common/reconstruction/include/ITSMFTReconstruction/PixelData.h
index 9b2c13b3db4fb..caccd646c85bc 100644
--- a/Detectors/ITSMFT/common/reconstruction/include/ITSMFTReconstruction/PixelData.h
+++ b/Detectors/ITSMFT/common/reconstruction/include/ITSMFTReconstruction/PixelData.h
@@ -273,6 +273,8 @@ class ChipPixelData
   std::vector<uint32_t>& getPixIds() { return mPixIds; }
   std::vector<int>& getPixelsOrder() { return mPixelsOrder; }
   uint32_t getOrderedPixId(int pos) const { return mPixIds[mPixelsOrder[pos]]; }
+  // Squashing can remove or reorder digits; otherwise their indices are contiguous.
+  uint32_t getDigitID(int pos) const { return mPixIds.empty() ? mStartID + pos : getOrderedPixId(pos); }
 
  private:
   uint8_t mROFlags = 0;                            // readout flags from the chip trailer
diff --git a/Detectors/ITSMFT/common/reconstruction/src/Clusterer.cxx b/Detectors/ITSMFT/common/reconstruction/src/Clusterer.cxx
index 2168c4b8d3308..23717e8b0a7f1 100644
--- a/Detectors/ITSMFT/common/reconstruction/src/Clusterer.cxx
+++ b/Detectors/ITSMFT/common/reconstruction/src/Clusterer.cxx
@@ -235,11 +235,7 @@ void Clusterer::ClustererThread::finishChip(ChipPixelData* curChipData, CompClus
       pixArrBuff.push_back(pix); // needed for cluster topology
       bbox.adjust(pix.getRowDirect(), pix.getCol());
       if (labelsClusPtr) {
-        if (parent->mSquashingDepth) { // the MCtruth for this pixel is stored in chip data: due to squashing we lose contiguity
-          fetchMCLabels(curChipData->getOrderedPixId(pixEntry.second), labelsDigPtr, nlab);
-        } else { // the MCtruth for this pixel is at curChipData->startID+pixEntry.second
-          fetchMCLabels(pixEntry.second + curChipData->getStartID(), labelsDigPtr, nlab);
-        }
+        fetchMCLabels(curChipData->getDigitID(pixEntry.second), labelsDigPtr, nlab);
       }
       next = pixEntry.first;
     }
@@ -256,11 +252,7 @@ void Clusterer::ClustererThread::finishChip(ChipPixelData* curChipData, CompClus
         pixArrBuff.push_back(pix);                 // needed for cluster topology
         bbox.adjust(pix.getRowDirect(), pix.getCol());
         if (labelsClusPtr) {
-          if (parent->mSquashingDepth) { // the MCtruth for this pixel is stored in chip data: due to squashing we lose contiguity
-            fetchMCLabels(curChipData->getOrderedPixId(pixEntry.second), labelsDigPtr, nlab);
-          } else { // the MCtruth for this pixel is at curChipData->startID+pixEntry.second
-            fetchMCLabels(pixEntry.second + curChipData->getStartID(), labelsDigPtr, nlab);
-          }
+          fetchMCLabels(curChipData->getDigitID(pixEntry.second), labelsDigPtr, nlab);
         }
         next = pixEntry.first;
       }
@@ -315,7 +307,7 @@ void Clusterer::ClustererThread::finishChipSingleHitFast(uint32_t hit, ChipPixel
 
   if (labelsClusPtr) { // MC labels were requested
     int nlab = 0;
-    fetchMCLabels(curChipData->getStartID() + hit, labelsDigPtr, nlab);
+    fetchMCLabels(curChipData->getDigitID(hit), labelsDigPtr, nlab);
     auto cnt = compClusPtr->size();
     for (int i = 0; i < nlab; i++) {
       labelsClusPtr->addElement(cnt, labelsBuff[i]);
@@ -437,6 +429,9 @@ void Clusterer::ClustererThread::updateChip(const ChipPixelData* curChipData, ui
 void Clusterer::ClustererThread::fetchMCLabels(int digID, const ConstMCTruth* labelsDig, int& nfilled)
 {
   // transfer MC labels to cluster
+  if (!labelsDig) {
+    return;
+  }
   auto sortBuffer = [this]() { std::sort(this->labelsBuff.begin(), this->labelsBuff.end(), [](Label const& a, Label const& b) { return a.getTrackID() < b.getTrackID(); }); };
   for (const auto& l : labelsDig->getLabels(digID)) {
     bool skip = false;
diff --git a/Detectors/Upgrades/ITS3/reconstruction/src/Clusterer.cxx b/Detectors/Upgrades/ITS3/reconstruction/src/Clusterer.cxx
index 60fc1859e4145..0491213aac72f 100644
--- a/Detectors/Upgrades/ITS3/reconstruction/src/Clusterer.cxx
+++ b/Detectors/Upgrades/ITS3/reconstruction/src/Clusterer.cxx
@@ -234,11 +234,7 @@ void Clusterer::ClustererThread::finishChip(ChipPixelData* curChipData, CompClus
       pixArrBuff.push_back(pix); // needed for cluster topology
       bbox.adjust(pix.getRowDirect(), pix.getCol());
       if (labelsClusPtr) {
-        if (parent->mSquashingDepth) { // the MCtruth for this pixel is stored in chip data: due to squashing we lose contiguity
-          fetchMCLabels(curChipData->getOrderedPixId(pixEntry.second), labelsDigPtr, nlab);
-        } else { // the MCtruth for this pixel is at curChipData->startID+pixEntry.second
-          fetchMCLabels(pixEntry.second + curChipData->getStartID(), labelsDigPtr, nlab);
-        }
+        fetchMCLabels(curChipData->getDigitID(pixEntry.second), labelsDigPtr, nlab);
       }
       next = pixEntry.first;
     }
@@ -255,11 +251,7 @@ void Clusterer::ClustererThread::finishChip(ChipPixelData* curChipData, CompClus
         pixArrBuff.push_back(pix);                 // needed for cluster topology
         bbox.adjust(pix.getRowDirect(), pix.getCol());
         if (labelsClusPtr) {
-          if (parent->mSquashingDepth) { // the MCtruth for this pixel is stored in chip data: due to squashing we lose contiguity
-            fetchMCLabels(curChipData->getOrderedPixId(pixEntry.second), labelsDigPtr, nlab);
-          } else { // the MCtruth for this pixel is at curChipData->startID+pixEntry.second
-            fetchMCLabels(pixEntry.second + curChipData->getStartID(), labelsDigPtr, nlab);
-          }
+          fetchMCLabels(curChipData->getDigitID(pixEntry.second), labelsDigPtr, nlab);
         }
         next = pixEntry.first;
       }
@@ -316,7 +308,7 @@ void Clusterer::ClustererThread::finishChipSingleHitFast(uint32_t hit, ChipPixel
 
   if (labelsClusPtr) { // MC labels were requested
     int nlab = 0;
-    fetchMCLabels(curChipData->getStartID() + hit, labelsDigPtr, nlab);
+    fetchMCLabels(curChipData->getDigitID(hit), labelsDigPtr, nlab);
     auto cnt = compClusPtr->size();
     for (int i = 0; i < nlab; i++) {
       labelsClusPtr->addElement(cnt, labelsBuff[i]);
@@ -454,6 +446,9 @@ void Clusterer::ClustererThread::updateChip(const ChipPixelData* curChipData, ui
 void Clusterer::ClustererThread::fetchMCLabels(int digID, const ConstMCTruth* labelsDig, int& nfilled)
 {
   // transfer MC labels to cluster
+  if (!labelsDig) {
+    return;
+  }
   auto sortBuffer = [this]() { std::sort(this->labelsBuff.begin(), this->labelsBuff.end(), [](Label const& a, Label const& b) { return a.getTrackID() < b.getTrackID(); }); };
   for (const auto& label : labelsDig->getLabels(digID)) {
     bool skip = false;