diff --git a/Geometry/GEMGeometryBuilder/interface/GEMGeometryParsFromDD.h b/Geometry/GEMGeometryBuilder/interface/GEMGeometryParsFromDD.h
index e4bd217ec17f1..b88a8ea70a47d 100644
--- a/Geometry/GEMGeometryBuilder/interface/GEMGeometryParsFromDD.h
+++ b/Geometry/GEMGeometryBuilder/interface/GEMGeometryParsFromDD.h
@@ -38,7 +38,10 @@ class GEMGeometryParsFromDD {
 
 private:
   // DD
-  void buildGeometry(DDFilteredView& fview, const MuonGeometryConstants& muonConstants, RecoIdealGeometry& rgeo);
+  void buildGeometry(DDFilteredView& fview,
+                     DDFilteredView& fview2,
+                     const MuonGeometryConstants& muonConstants,
+                     RecoIdealGeometry& rgeo);
   void buildSuperChamber(DDFilteredView& fv, GEMDetId detId, RecoIdealGeometry& rgeo);
   void buildChamber(DDFilteredView& fv, GEMDetId detId, RecoIdealGeometry& rgeo);
   void buildEtaPartition(DDFilteredView& fv, GEMDetId detId, RecoIdealGeometry& rgeo);
diff --git a/Geometry/GEMGeometryBuilder/src/GEMGeometryParsFromDD.cc b/Geometry/GEMGeometryBuilder/src/GEMGeometryParsFromDD.cc
index 17ef0b5492486..4d8712b6420a2 100644
--- a/Geometry/GEMGeometryBuilder/src/GEMGeometryParsFromDD.cc
+++ b/Geometry/GEMGeometryBuilder/src/GEMGeometryParsFromDD.cc
@@ -43,11 +43,13 @@ void GEMGeometryParsFromDD::build(const DDCompactView* cview,
   // Asking only for the MuonGEM's
   DDSpecificsMatchesValueFilter filter{DDValue(attribute, value, 0.0)};
   DDFilteredView fv(*cview, filter);
+  DDFilteredView fv2(*cview, filter);
 
-  this->buildGeometry(fv, muonConstants, rgeo);
+  this->buildGeometry(fv, fv2, muonConstants, rgeo);
 }
 
 void GEMGeometryParsFromDD::buildGeometry(DDFilteredView& fv,
+                                          DDFilteredView& fvGE2,
                                           const MuonGeometryConstants& muonConstants,
                                           RecoIdealGeometry& rgeo) {
   LogDebug("GEMGeometryParsFromDD") << "Building the geometry service";
@@ -58,46 +60,83 @@ void GEMGeometryParsFromDD::buildGeometry(DDFilteredView& fv,
   MuonGeometryNumbering muonDDDNumbering(muonConstants);
   GEMNumberingScheme gemNumbering(muonConstants);
 
-  bool doSuper = fv.firstChild();
+  // Check for the demonstrator geometry (only 1 chamber of GE2/1)
+  int nGE21 = 0;
+  bool doSuper = fvGE2.firstChild();
+  while (doSuper) {
+    // getting chamber id from eta partitions
+    fvGE2.firstChild();
+    doSuper = fvGE2.firstChild();
+    if (doSuper) {
+      int rawidCh = gemNumbering.baseNumberToUnitNumber(muonDDDNumbering.geoHistoryToBaseNumber(fvGE2.geoHistory()));
+      GEMDetId detIdCh = GEMDetId(rawidCh);
+      if (detIdCh.station() == 2)
+        nGE21++;
+
+      // back to chambers
+      fvGE2.parent();
+      fvGE2.parent();
+      doSuper = (nGE21 < 2 && fvGE2.nextSibling());
+    } else {
+      edm::LogError("GEMGeometryParsFromDD") << "Failed to find next child volume. Cannot determine presence of GE 2/1";
+    }
+  }
+  bool demonstratorGeometry = nGE21 == 1;
+
+#ifdef EDM_ML_DEBUG
+  edm::LogVerbatim("Geometry") << "Found " << nGE21 << " GE2/1 chambers. Demonstrator geometry on? "
+                               << demonstratorGeometry;
+#endif
+
+  doSuper = fv.firstChild();
 
   LogDebug("GEMGeometryParsFromDD") << "doSuperChamber = " << doSuper;
   // loop over superchambers
   while (doSuper) {
     // getting chamber id from eta partitions
     fv.firstChild();
-    fv.firstChild();
-    GEMDetId detIdCh =
-        GEMDetId(gemNumbering.baseNumberToUnitNumber(muonDDDNumbering.geoHistoryToBaseNumber(fv.geoHistory())));
-    // back to chambers
-    fv.parent();
-    fv.parent();
-
-    // currently there is no superchamber in the geometry
-    // only 2 chambers are present separated by a gap.
-    // making superchamber out of the first chamber layer including the gap between chambers
-    if (detIdCh.layer() == 1) {  // only make superChambers when doing layer 1
-      buildSuperChamber(fv, detIdCh, rgeo);
-    }
-    buildChamber(fv, detIdCh, rgeo);
-
-    // loop over chambers
-    // only 1 chamber
-    bool doChambers = fv.firstChild();
-    while (doChambers) {
-      // loop over GEMEtaPartitions
-      bool doEtaPart = fv.firstChild();
-      while (doEtaPart) {
-        GEMDetId detId =
-            GEMDetId(gemNumbering.baseNumberToUnitNumber(muonDDDNumbering.geoHistoryToBaseNumber(fv.geoHistory())));
-        buildEtaPartition(fv, detId, rgeo);
+    doSuper = fv.firstChild();
+    if (doSuper) {
+      GEMDetId detIdCh =
+          GEMDetId(gemNumbering.baseNumberToUnitNumber(muonDDDNumbering.geoHistoryToBaseNumber(fv.geoHistory())));
+      // back to chambers
+      fv.parent();
+      fv.parent();
+
+      // currently there is no superchamber in the geometry
+      // only 2 chambers are present separated by a gap.
+      // making superchamber out of the first chamber layer including the gap between chambers
 
-        doEtaPart = fv.nextSibling();
+      // In Run 3 we also have a single GE2/1 chamber at layer 2. We
+      // make sure the superchamber gets built but also we build on the
+      // first layer for the other stations so the superchamber is in
+      // the right position there.
+      if ((detIdCh.layer() == 1) || (detIdCh.layer() == 2 and detIdCh.station() == 2 and demonstratorGeometry)) {
+        buildSuperChamber(fv, detIdCh, rgeo);
+      }
+      buildChamber(fv, detIdCh, rgeo);
+
+      // loop over chambers
+      // only 1 chamber
+      bool doChambers = fv.firstChild();
+      while (doChambers) {
+        // loop over GEMEtaPartitions
+        bool doEtaPart = fv.firstChild();
+        while (doEtaPart) {
+          GEMDetId detId =
+              GEMDetId(gemNumbering.baseNumberToUnitNumber(muonDDDNumbering.geoHistoryToBaseNumber(fv.geoHistory())));
+          buildEtaPartition(fv, detId, rgeo);
+
+          doEtaPart = fv.nextSibling();
+        }
+        fv.parent();
+        doChambers = fv.nextSibling();
       }
       fv.parent();
-      doChambers = fv.nextSibling();
+      doSuper = fv.nextSibling();
+    } else {
+      edm::LogError("GEMGeometryParsFromDD") << "Failed to find next child volume. Cannot build GEM chambers.";
     }
-    fv.parent();
-    doSuper = fv.nextSibling();
   }
 }
 
@@ -246,6 +285,24 @@ void GEMGeometryParsFromDD::buildGeometry(cms::DDFilteredView& fv,
   int theRingLevel = muonConstants.getValue("mg_ring") / theLevelPart;
   int theSectorLevel = muonConstants.getValue("mg_sector") / theLevelPart;
 
+  // Check for the demonstrator geometry (only 1 chamber of GE2/1)
+  auto start = fv.copyNos();
+  int nGE21 = 0;
+  while (nGE21 < 2 && fv.firstChild()) {
+    const auto& history = fv.history();
+    MuonBaseNumber num(mdddnum.geoHistoryToBaseNumber(history));
+    GEMDetId detId(gemNum.baseNumberToUnitNumber(num));
+    if (fv.level() == levelChamb && detId.station() == 2) {
+      nGE21++;
+    }
+  }
+  bool demonstratorGeometry = nGE21 == 1;
+#ifdef EDM_ML_DEBUG
+  edm::LogVerbatim("Geometry") << "Found " << nGE21 << " GE2/1 chambers. Demonstrator geometry on? "
+                               << demonstratorGeometry;
+#endif
+
+  fv.goTo(start);
   while (fv.firstChild()) {
     const auto& history = fv.history();
     MuonBaseNumber num(mdddnum.geoHistoryToBaseNumber(history));
@@ -267,7 +324,7 @@ void GEMGeometryParsFromDD::buildGeometry(cms::DDFilteredView& fv,
       }
     } else {
       if (fv.level() == levelChamb) {
-        if (detId.layer() == 1) {
+        if ((detId.layer() == 1) || (detId.layer() == 2 and detId.station() == 2 and demonstratorGeometry)) {
           buildSuperChamber(fv, detId, rgeo);
         }
         buildChamber(fv, detId, rgeo);