diff --git a/Modules/PHOS/src/CalibQcTask.cxx b/Modules/PHOS/src/CalibQcTask.cxx
index 9227d92ed4..d7c8d251c1 100644
--- a/Modules/PHOS/src/CalibQcTask.cxx
+++ b/Modules/PHOS/src/CalibQcTask.cxx
@@ -263,7 +263,7 @@ void CalibQcTask::monitorData(o2::framework::ProcessingContext& ctx)
   if (mMode == 0) { // Bad map
     if (hasCalibDiff) {
       auto diff = ctx.inputs().get<gsl::span<short>>("calibdiff");
-      char relid[3];
+      int8_t relid[3];
       for (short absId = o2::phos::Mapping::NCHANNELS; absId > 1792; absId--) {
         o2::phos::Geometry::absToRelNumbering(absId, relid);
         mHist2D[kChangeHGM1 + relid[0] - 1]->SetBinContent(relid[1], relid[2], diff[absId]);
@@ -272,7 +272,7 @@ void CalibQcTask::monitorData(o2::framework::ProcessingContext& ctx)
   } else if (mMode == 1) { // Pedestal
     if (hasCalibDiff) {
       auto diff = ctx.inputs().get<gsl::span<short>>("calibdiff");
-      char relid[3];
+      int8_t relid[3];
       for (short absId = o2::phos::Mapping::NCHANNELS; absId > 1792; absId--) {
         o2::phos::Geometry::absToRelNumbering(absId, relid);
         mHist2D[kChangeHGM1 + relid[0] - 1]->SetBinContent(relid[1], relid[2], diff[absId]);
@@ -281,7 +281,7 @@ void CalibQcTask::monitorData(o2::framework::ProcessingContext& ctx)
     }
     if (hasPedestals) {
       auto peds = o2::framework::DataRefUtils::as<o2::framework::CCDBSerialized<o2::phos::Pedestals>>(ctx.inputs().get<o2::framework::DataRef>("peds"));
-      char relid[3];
+      int8_t relid[3];
       for (short absId = o2::phos::Mapping::NCHANNELS; absId > 1792; absId--) {
         o2::phos::Geometry::absToRelNumbering(absId, relid);
         mHist2D[kValueHGM1 + relid[0] - 1]->SetBinContent(relid[1], relid[2], peds->getHGPedestal(absId));
@@ -293,7 +293,7 @@ void CalibQcTask::monitorData(o2::framework::ProcessingContext& ctx)
   } else if (mMode == 2) { // LED
     if (hasCalibDiff) {
       auto diff = ctx.inputs().get<gsl::span<float>>("calibdiff");
-      char relid[3];
+      int8_t relid[3];
       for (short absId = o2::phos::Mapping::NCHANNELS; absId > 1792; absId--) {
         o2::phos::Geometry::absToRelNumbering(absId, relid);
         mHist2D[kChangeHGM1 + relid[0] - 1]->SetBinContent(relid[1], relid[2], diff[absId]);
@@ -301,7 +301,7 @@ void CalibQcTask::monitorData(o2::framework::ProcessingContext& ctx)
     }
     if (hasCalibPars) {
       auto calibParams = o2::framework::DataRefUtils::as<o2::framework::CCDBSerialized<o2::phos::CalibParams>>(ctx.inputs().get<o2::framework::DataRef>("calibpars"));
-      char relid[3];
+      int8_t relid[3];
       for (short absId = o2::phos::Mapping::NCHANNELS; absId > 1792; absId--) {
         o2::phos::Geometry::absToRelNumbering(absId, relid);
         mHist2D[kValueHGM1 + relid[0] - 1]->SetBinContent(relid[1], relid[2], calibParams->getHGLGRatio(absId));
diff --git a/Modules/PHOS/src/ClusterCheck.cxx b/Modules/PHOS/src/ClusterCheck.cxx
index 96d4739727..c0c0dfa49a 100644
--- a/Modules/PHOS/src/ClusterCheck.cxx
+++ b/Modules/PHOS/src/ClusterCheck.cxx
@@ -126,7 +126,7 @@ Quality ClusterCheck::check(std::map<std::string, std::shared_ptr<MonitorObject>
       for (int ix = 1; ix <= 64; ix++) {
         for (int iz = 1; iz <= 56; iz++) {
           float cont = h->GetBinContent(ix, iz);
-          char relid[3] = { char(m), char(ix), char(iz) };
+          int8_t relid[3] = { int8_t(m), int8_t(ix), int8_t(iz) };
           short absId;
           o2::phos::Geometry::relToAbsNumbering(relid, absId);
           if (cont > 0) {
diff --git a/Modules/PHOS/src/ClusterQcTask.cxx b/Modules/PHOS/src/ClusterQcTask.cxx
index 2a29ae249d..e8394368c8 100644
--- a/Modules/PHOS/src/ClusterQcTask.cxx
+++ b/Modules/PHOS/src/ClusterQcTask.cxx
@@ -167,7 +167,7 @@ void ClusterQcTask::monitorData(o2::framework::ProcessingContext& ctx)
       // Fill occupancy and time-E histos
       float posX, posZ;
       clu.getLocalPosition(posX, posZ);
-      char relid[3];
+      int8_t relid[3];
       mGeom->relPosToRelId(mod, posX, posZ, relid);
 
       if (e > mOccCut) {
diff --git a/Modules/PHOS/src/RawQcTask.cxx b/Modules/PHOS/src/RawQcTask.cxx
index 26e679b782..02b9597b9b 100644
--- a/Modules/PHOS/src/RawQcTask.cxx
+++ b/Modules/PHOS/src/RawQcTask.cxx
@@ -280,7 +280,7 @@ void RawQcTask::monitorData(o2::framework::ProcessingContext& ctx)
       address &= ~(1 << 14); // remove HG/LG bit 14
       float chi = 0.2 * (*it);
       it++;
-      char relid[3];
+      int8_t relid[3];
       o2::phos::Geometry::absToRelNumbering(address, relid);
       mHist2D[kChi2M1 + relid[0] - 1]->Fill(relid[1] - 0.5, relid[2] - 0.5, chi);
       mHist2D[kChi2NormM1 + relid[0] - 1]->Fill(relid[1] - 0.5, relid[2] - 0.5);
@@ -393,7 +393,7 @@ void RawQcTask::endOfCycle()
     ILOG(Info, Support) << " Caclulating number of peaks" << ENDM;
     for (unsigned int absId = 1793; absId <= o2::phos::Mapping::NCHANNELS; absId++) {
       int npeaks = mSpSearcher->Search(&(mSpectra[absId - 1793]), 2, "goff", 0.1);
-      char relid[3];
+      int8_t relid[3];
       o2::phos::Geometry::absToRelNumbering(absId, relid);
       short mod = relid[0] - 1;
       int ibin = mHist2DMean[kLEDNpeaksM1 + mod]->FindBin(relid[1] - 0.5, relid[2] - 0.5);
@@ -446,7 +446,7 @@ void RawQcTask::FillTRUHistograms(const gsl::span<const o2::phos::Cell>& cells,
 {
   std::vector<int> triggerSTTiles;
   std::vector<int> triggerDGTiles;
-  char relId[3] = { 0 };
+  int8_t relId[3] = { 0 };
   for (const auto tr : cellsTR) {
     triggerSTTiles.clear();
     triggerDGTiles.clear();
@@ -534,7 +534,7 @@ void RawQcTask::FillPhysicsHistograms(const gsl::span<const o2::phos::Cell>& cel
         //  relid[0] = PHOS Module number 1,...4:module
         //  relid[1] = Row number inside a PHOS module (Phi coordinate)
         //  relid[2] = Column number inside a PHOS module (Z coordinate)
-        char relid[3];
+        int8_t relid[3];
         o2::phos::Geometry::absToRelNumbering(address, relid);
         short mod = relid[0] - 1;
         int ibin = 0;
@@ -575,7 +575,7 @@ void RawQcTask::FillPedestalHistograms(const gsl::span<const o2::phos::Cell>& ce
     for (int i = firstCellInEvent; i < lastCellInEvent; i++) {
       const o2::phos::Cell c = cells[i];
       short address = c.getAbsId();
-      char relid[3];
+      int8_t relid[3];
       o2::phos::Geometry::absToRelNumbering(address, relid);
       short mod = relid[0] - 1;
       if (c.getHighGain()) {