diff --git a/root/io/hadd/CMakeLists.txt b/root/io/hadd/CMakeLists.txt
index 0dfc9cbce7..d188050f5a 100644
--- a/root/io/hadd/CMakeLists.txt
+++ b/root/io/hadd/CMakeLists.txt
@@ -1,11 +1,17 @@
 if(ROOT_pyroot_FOUND)
     ROOTTEST_ADD_TEST(compression_settings
                       MACRO test_compression_settings.py)
-
     ROOTTEST_ADD_TEST(input_validation
                       MACRO input_validation.py)
 endif()
 
+ROOTTEST_ADD_TEST(test_MergeChangeComp
+                  COPY_TO_BUILDDIR merge_gen_input_tuples.C merge_changeComp_check_output.C
+                  PRECMD ${ROOT_root_CMD} -q -b -l "merge_gen_input_tuples.C(\"test_comp_in1.root\", \"test_comp_in2.root\")"
+                  COMMAND ${ROOT_hadd_CMD} -f404 test_comp_out.root test_comp_in1.root test_comp_in2.root
+                  POSTCMD ${ROOT_root_CMD} -q -b -l "merge_changeComp_check_output.C(404, \"test_comp_out.root\", \"test_comp_in1.root\", \"test_comp_in2.root\")"
+)
+
 ROOTTEST_ADD_TEST(test_TreeChangeComp
                   COPY_TO_BUILDDIR hadd_gen_input_tree.C hadd_check_comp_tree.C
                   PRECMD ${ROOT_root_CMD} -q -b -l "hadd_gen_input_tree.C(\"test_comp_tree_in.root\")"
diff --git a/root/io/hadd/Testing/Temporary/CTestCostData.txt b/root/io/hadd/Testing/Temporary/CTestCostData.txt
new file mode 100644
index 0000000000..ed97d539c0
--- /dev/null
+++ b/root/io/hadd/Testing/Temporary/CTestCostData.txt
@@ -0,0 +1 @@
+---
diff --git a/root/io/hadd/foo.root b/root/io/hadd/foo.root
new file mode 100644
index 0000000000..39f141c14b
Binary files /dev/null and b/root/io/hadd/foo.root differ
diff --git a/root/io/hadd/merge_changeComp_check_output.C b/root/io/hadd/merge_changeComp_check_output.C
new file mode 100644
index 0000000000..a8e3ee6062
--- /dev/null
+++ b/root/io/hadd/merge_changeComp_check_output.C
@@ -0,0 +1,63 @@
+#include <ROOT/RLogger.hxx>
+#include <ROOT/RNTupleModel.hxx>
+#include <ROOT/RNTupleReader.hxx>
+#include <ROOT/RNTupleWriter.hxx>
+#include <ROOT/RPageStorageFile.hxx>
+#include <Compression.h>
+#include <RZip.h>
+
+#include <TSystem.h>
+
+int merge_changeComp_check_output(int expectedCompression, const char *fnameOut, const char *fnameIn1,
+                                  const char *fnameIn2)
+{
+   using namespace ROOT::Experimental;
+
+   auto noPrereleaseWarning = RLogScopedVerbosity(NTupleLog(), ROOT::Experimental::ELogLevel::kError);
+
+   Internal::RPageSourceFile source("ntpl", fnameOut, RNTupleReadOptions());
+   source.Attach();
+
+   Internal::RClusterPool pool{source};
+
+   const auto expCompAlgo = ROOT::RCompressionSetting::AlgorithmFromCompressionSettings(expectedCompression);
+   const auto &desc = source.GetSharedDescriptorGuard();
+   auto clusterIter = desc->GetClusterIterable();
+   for (const auto &clusterDesc : clusterIter) {
+      // check advertised compression
+      int advertisedCompression = clusterDesc.GetColumnRange(0).fCompressionSettings;
+      if (advertisedCompression != expectedCompression) {
+         std::cerr << "Expected advertised compression to be " << expectedCompression << " but it is "
+                   << advertisedCompression << "\n";
+         return 1;
+      }
+
+      // check actual compression
+      for (const auto &column : desc->GetColumnIterable()) {
+         const auto &pages = clusterDesc.GetPageRange(column.GetLogicalId());
+         std::uint64_t pageIdx = 0;
+         for (const auto &pageInfo : pages.fPageInfos) {
+            std::vector<Internal::RCluster::RKey> keys{clusterDesc.GetId(), {column.GetPhysicalId()}};
+            auto cluster = pool.GetCluster(clusterDesc.GetId(), {column.GetPhysicalId()});
+            Internal::ROnDiskPage::Key key{column.GetPhysicalId(), pageIdx};
+            auto onDiskPage = cluster->GetOnDiskPage(key);
+            R__ASSERT(onDiskPage);
+            const auto actualCompAlgo =
+               R__getCompressionAlgorithm((const unsigned char *)onDiskPage->GetAddress(), onDiskPage->GetSize());
+            if (actualCompAlgo != expCompAlgo) {
+               std::cerr << "Expected actual compression to be "
+                         << ROOT::RCompressionSetting::AlgorithmToString(expCompAlgo) << " but it is "
+                         << ROOT::RCompressionSetting::AlgorithmToString(actualCompAlgo) << "\n";
+               return 1;
+            }
+            ++pageIdx;
+         }
+      }
+   }
+
+   gSystem->Unlink(fnameOut);
+   gSystem->Unlink(fnameIn1);
+   gSystem->Unlink(fnameIn2);
+
+   return 0;
+}
diff --git a/root/io/hadd/merge_gen_input_tuples.C b/root/io/hadd/merge_gen_input_tuples.C
new file mode 100644
index 0000000000..f320422e40
--- /dev/null
+++ b/root/io/hadd/merge_gen_input_tuples.C
@@ -0,0 +1,45 @@
+#include <ROOT/RLogger.hxx>
+#include <ROOT/RNTupleModel.hxx>
+#include <ROOT/RNTupleReader.hxx>
+#include <ROOT/RNTupleWriter.hxx>
+#include <ROOT/RPageStorageFile.hxx>
+#include <Compression.h>
+
+#include <TSystem.h>
+
+#include <string>
+#include <utility>
+
+void merge_gen_input_tuples(const char *fname1 = "test_rntuple_input1.root", const char *fname2 = "test_rntuple_input2.root")
+{
+   using namespace ROOT::Experimental;
+   
+   auto noPrereleaseWarning = RLogScopedVerbosity(NTupleLog(), ROOT::Experimental::ELogLevel::kError);
+
+   {
+      auto model = RNTupleModel::Create();
+      auto fi = model->MakeField<int>("I", 1337);
+      auto fl = model->MakeField<long>("L", 666);
+      auto opts = RNTupleWriteOptions{};
+      opts.SetCompression(ROOT::CompressionSettings(ROOT::RCompressionSetting::EAlgorithm::kZSTD, 5));
+      auto writer = RNTupleWriter::Recreate(std::move(model), "ntpl", fname1, opts);
+      for (int i = 0; i < 1000; ++i) {
+         *fi = i;
+         *fl = i;
+         writer->Fill();
+      }
+   }
+   {
+      auto model = RNTupleModel::Create();
+      auto fi = model->MakeField<int>("I", 123);
+      auto fl = model->MakeField<long>("L", 420);
+      auto opts = RNTupleWriteOptions{};
+      opts.SetCompression(ROOT::CompressionSettings(ROOT::RCompressionSetting::EAlgorithm::kZLIB, 1));
+      auto writer = RNTupleWriter::Recreate(std::move(model), "ntpl", fname2, opts);
+      for (int i = 0; i < 100; ++i) {
+         *fi = i;
+         *fl = i;
+         writer->Fill();
+      }
+   }
+}