diff --git a/tree/ntuple/v7/inc/ROOT/RNTupleMerger.hxx b/tree/ntuple/v7/inc/ROOT/RNTupleMerger.hxx
index 74f5c5165d7bf..934b900ec62c6 100644
--- a/tree/ntuple/v7/inc/ROOT/RNTupleMerger.hxx
+++ b/tree/ntuple/v7/inc/ROOT/RNTupleMerger.hxx
@@ -86,6 +86,7 @@ struct RNTupleMergeOptions {
  */
 // clang-format on
 class RNTupleMerger final {
+   std::unique_ptr<RPageSink> fDestination;
    std::unique_ptr<RPageAllocator> fPageAlloc;
    std::optional<TTaskGroup> fTaskGroup;
 
@@ -97,11 +98,11 @@ class RNTupleMerger final {
                             std::span<RColumnMergeInfo> extraDstColumns, RNTupleMergeData &mergeData);
 
 public:
-   RNTupleMerger();
+   /// Creates a RNTupleMerger with the given destination.
+   explicit RNTupleMerger(std::unique_ptr<RPageSink> destination);
 
    /// Merge a given set of sources into the destination.
-   RResult<void> Merge(std::span<RPageSource *> sources, RPageSink &destination,
-                       const RNTupleMergeOptions &mergeOpts = RNTupleMergeOptions());
+   RResult<void> Merge(std::span<RPageSource *> sources, const RNTupleMergeOptions &mergeOpts = RNTupleMergeOptions());
 
 }; // end of class RNTupleMerger
 
diff --git a/tree/ntuple/v7/src/RNTupleMerger.cxx b/tree/ntuple/v7/src/RNTupleMerger.cxx
index 0852e27bf1767..48a8ab1db6ef2 100644
--- a/tree/ntuple/v7/src/RNTupleMerger.cxx
+++ b/tree/ntuple/v7/src/RNTupleMerger.cxx
@@ -215,7 +215,7 @@ try {
    }
 
    // Now merge
-   RNTupleMerger merger;
+   RNTupleMerger merger{std::move(destination)};
    RNTupleMergeOptions mergerOpts;
    mergerOpts.fCompressionSettings = *compression;
    mergerOpts.fExtraVerbose = extraVerbose;
@@ -225,7 +225,7 @@ try {
    if (auto errBehavior = ParseOptionErrBehavior(mergeInfo->fOptions)) {
       mergerOpts.fErrBehavior = *errBehavior;
    }
-   merger.Merge(sourcePtrs, *destination, mergerOpts).ThrowOnError();
+   merger.Merge(sourcePtrs, mergerOpts).ThrowOnError();
 
    // Provide the caller with a merged anchor object (even though we've already
    // written it).
@@ -928,23 +928,28 @@ GatherColumnInfos(const RDescriptorsComparison &descCmp, const RNTupleDescriptor
    return res;
 }
 
-RNTupleMerger::RNTupleMerger()
+RNTupleMerger::RNTupleMerger(std::unique_ptr<RPageSink> destination)
    // TODO(gparolini): consider using an arena allocator instead, since we know the precise lifetime
    // of the RNTuples we are going to handle (e.g. we can reset the arena at every source)
-   : fPageAlloc(std::make_unique<RPageAllocatorHeap>())
+   : fDestination(std::move(destination)), fPageAlloc(std::make_unique<RPageAllocatorHeap>())
 {
+   R__ASSERT(fDestination);
+
 #ifdef R__USE_IMT
    if (ROOT::IsImplicitMTEnabled())
       fTaskGroup = TTaskGroup();
 #endif
 }
 
-ROOT::RResult<void>
-RNTupleMerger::Merge(std::span<RPageSource *> sources, RPageSink &destination, const RNTupleMergeOptions &mergeOptsIn)
+ROOT::RResult<void> RNTupleMerger::Merge(std::span<RPageSource *> sources, const RNTupleMergeOptions &mergeOptsIn)
 {
    RNTupleMergeOptions mergeOpts = mergeOptsIn;
+
+   assert(fDestination);
+
+   // Set compression settings if unset and verify it's compatible with the sink
    {
-      const auto dstCompSettings = destination.GetWriteOptions().GetCompression();
+      const auto dstCompSettings = fDestination->GetWriteOptions().GetCompression();
       if (!mergeOpts.fCompressionSettings) {
          mergeOpts.fCompressionSettings = dstCompSettings;
       } else if (*mergeOpts.fCompressionSettings != dstCompSettings) {
@@ -955,7 +960,7 @@ RNTupleMerger::Merge(std::span<RPageSource *> sources, RPageSink &destination, c
       }
    }
 
-   RNTupleMergeData mergeData{sources, destination, mergeOpts};
+   RNTupleMergeData mergeData{sources, *fDestination, mergeOpts};
 
    std::unique_ptr<RNTupleModel> model; // used to initialize the schema of the output RNTuple
 
@@ -976,20 +981,20 @@ RNTupleMerger::Merge(std::span<RPageSource *> sources, RPageSink &destination, c
       mergeData.fSrcDescriptor = &srcDescriptor.GetRef();
 
       // Create sink from the input model if not initialized
-      if (!destination.IsInitialized()) {
+      if (!fDestination->IsInitialized()) {
          auto opts = RNTupleDescriptor::RCreateModelOptions();
          opts.fReconstructProjections = true;
          model = srcDescriptor->CreateModel(opts);
-         destination.Init(*model);
+         fDestination->Init(*model);
       }
 
       for (const auto &extraTypeInfoDesc : srcDescriptor->GetExtraTypeInfoIterable())
-         destination.UpdateExtraTypeInfo(extraTypeInfoDesc);
+         fDestination->UpdateExtraTypeInfo(extraTypeInfoDesc);
 
       auto descCmpRes = CompareDescriptorStructure(mergeData.fDstDescriptor, srcDescriptor.GetRef());
       if (!descCmpRes) {
          SKIP_OR_ABORT(
-            std::string("Source RNTuple will be skipped due to incompatible schema with the destination:\n") +
+            std::string("Source RNTuple will be skipped due to incompatible schema with the fDestination:\n") +
             descCmpRes.GetError()->GetReport());
       }
       auto descCmp = descCmpRes.Unwrap();
@@ -1011,7 +1016,7 @@ RNTupleMerger::Merge(std::span<RPageSource *> sources, RPageSink &destination, c
             ExtendDestinationModel(descCmp.fExtraSrcFields, *model, mergeData, descCmp.fCommonFields);
          } else if (mergeOpts.fMergingMode == ENTupleMergingMode::kStrict) {
             // If the current source has extra fields and we're in Strict mode, error
-            std::string msg = "Source RNTuple has extra fields that the destination RNTuple doesn't have:";
+            std::string msg = "Source RNTuple has extra fields that the fDestination RNTuple doesn't have:";
             for (const auto *field : descCmp.fExtraSrcFields) {
                msg += "\n  " + field->GetFieldName() + " : " + field->GetTypeName();
             }
@@ -1025,8 +1030,8 @@ RNTupleMerger::Merge(std::span<RPageSource *> sources, RPageSink &destination, c
    } // end loop over sources
 
    // Commit the output
-   destination.CommitClusterGroup();
-   destination.CommitDataset();
+   fDestination->CommitClusterGroup();
+   fDestination->CommitDataset();
 
    return RResult<void>::Success();
 }
diff --git a/tree/ntuple/v7/test/ntuple_checksum.cxx b/tree/ntuple/v7/test/ntuple_checksum.cxx
index c469aa4b63d7c..78294a0033973 100644
--- a/tree/ntuple/v7/test/ntuple_checksum.cxx
+++ b/tree/ntuple/v7/test/ntuple_checksum.cxx
@@ -147,9 +147,9 @@ TEST(RNTupleChecksum, Merge)
    }
 
    auto destination = std::make_unique<RPageSinkFile>("ntpl", fileGuard3.GetPath(), options);
-   RNTupleMerger merger;
+   RNTupleMerger merger{std::move(destination)};
    try {
-      merger.Merge(sourcePtrs, *destination);
+      merger.Merge(sourcePtrs);
       FAIL() << "merging should fail due to checksum error";
    } catch (const ROOT::RException &e) {
       EXPECT_THAT(e.what(), testing::HasSubstr("page checksum"));
diff --git a/tree/ntuple/v7/test/ntuple_merger.cxx b/tree/ntuple/v7/test/ntuple_merger.cxx
index 669c8c5c69e8a..948a09506d0f6 100644
--- a/tree/ntuple/v7/test/ntuple_merger.cxx
+++ b/tree/ntuple/v7/test/ntuple_merger.cxx
@@ -133,24 +133,26 @@ TEST(RNTupleMerger, MergeSymmetric)
       }
 
       // Now Merge the inputs
-      RNTupleMerger merger;
       RNTupleMergeOptions opts;
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kFilter;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_TRUE(bool(res));
       }
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kUnion;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_TRUE(bool(res));
       }
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kStrict;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_TRUE(bool(res));
       }
    }
@@ -238,12 +240,12 @@ TEST(RNTupleMerger, MergeAsymmetric1)
 
       // Now Merge the inputs
       // We expect this to fail in Filter and Strict mode since the fields between the sources do NOT match
-      RNTupleMerger merger;
       RNTupleMergeOptions opts;
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kFilter;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_FALSE(res);
          if (res.GetError()) {
             EXPECT_THAT(res.GetError()->GetReport(), testing::HasSubstr("missing the following field"));
@@ -252,7 +254,8 @@ TEST(RNTupleMerger, MergeAsymmetric1)
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kStrict;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_FALSE(res);
          if (res.GetError()) {
             EXPECT_THAT(res.GetError()->GetReport(), testing::HasSubstr("missing the following field"));
@@ -261,7 +264,8 @@ TEST(RNTupleMerger, MergeAsymmetric1)
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kUnion;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_TRUE(bool(res));
       }
    }
@@ -308,12 +312,12 @@ TEST(RNTupleMerger, MergeAsymmetric2)
 
       // Now Merge the inputs
       // We expect this to fail in Filter and Strict mode since the fields between the sources do NOT match
-      RNTupleMerger merger;
       RNTupleMergeOptions opts;
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kFilter;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_FALSE(res);
          if (res.GetError()) {
             EXPECT_THAT(res.GetError()->GetReport(), testing::HasSubstr("missing the following field"));
@@ -322,7 +326,8 @@ TEST(RNTupleMerger, MergeAsymmetric2)
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kStrict;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_FALSE(res);
          if (res.GetError()) {
             EXPECT_THAT(res.GetError()->GetReport(), testing::HasSubstr("missing the following field"));
@@ -331,7 +336,8 @@ TEST(RNTupleMerger, MergeAsymmetric2)
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kUnion;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_TRUE(bool(res));
       }
    }
@@ -378,12 +384,12 @@ TEST(RNTupleMerger, MergeAsymmetric3)
 
       // Now Merge the inputs
       // We expect this to succeed except in all modes except Strict.
-      RNTupleMerger merger;
       RNTupleMergeOptions opts;
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kStrict;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_FALSE(res);
          if (res.GetError()) {
             EXPECT_THAT(res.GetError()->GetReport(), testing::HasSubstr("Source RNTuple has extra fields"));
@@ -392,13 +398,15 @@ TEST(RNTupleMerger, MergeAsymmetric3)
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kFilter;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_TRUE(bool(res));
       }
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
          opts.fMergingMode = ENTupleMergingMode::kUnion;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_TRUE(bool(res));
       }
    }
@@ -463,10 +471,10 @@ TEST(RNTupleMerger, MergeVector)
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), opts);
 
          // Now Merge the inputs
-         RNTupleMerger merger;
          RNTupleMergeOptions mopts;
          mopts.fMergingMode = mmode;
-         auto res = merger.Merge(sourcePtrs, *destination, mopts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, mopts);
          EXPECT_TRUE(bool(res));
       }
 
@@ -558,14 +566,14 @@ TEST(RNTupleMerger, MergeInconsistentTypes)
 
       // Create the output
       auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), RNTupleWriteOptions());
+      RNTupleMerger merger{std::move(destination)};
 
       // Now Merge the inputs
       // We expect this to fail since the fields between the sources do NOT match
       for (const auto mmode : {ENTupleMergingMode::kFilter, ENTupleMergingMode::kStrict, ENTupleMergingMode::kUnion}) {
-         RNTupleMerger merger;
          RNTupleMergeOptions opts;
          opts.fMergingMode = mmode;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_FALSE(res);
          if (res.GetError()) {
             EXPECT_THAT(res.GetError()->GetReport(), testing::HasSubstr("type incompatible"));
@@ -877,19 +885,30 @@ TEST(RNTupleMerger, ChangeCompression)
       auto destinationUncomp = std::make_unique<RPageSinkFile>("ntuple", fileGuardOutUncomp.GetPath(), writeOpts);
       writeOpts.SetEnablePageChecksums(false);
 
-      RNTupleMerger merger;
       auto opts = RNTupleMergeOptions{};
       opts.fCompressionSettings = kNewComp;
-      // This should fail because we specified a different compression than the sink
-      auto res = merger.Merge(sourcePtrs, *destinationDifferentComp, opts);
-      EXPECT_FALSE(bool(res));
-      res = merger.Merge(sourcePtrs, *destinationChecksum, opts);
-      EXPECT_TRUE(bool(res));
-      res = merger.Merge(sourcePtrs, *destinationNoChecksum, opts);
-      EXPECT_TRUE(bool(res));
-      opts.fCompressionSettings = 0;
-      res = merger.Merge(sourcePtrs, *destinationUncomp, opts);
-      EXPECT_TRUE(bool(res));
+      {
+         RNTupleMerger merger{std::move(destinationDifferentComp)};
+         // This should fail because we specified a different compression than the sink
+         auto res = merger.Merge(sourcePtrs, opts);
+         EXPECT_FALSE(bool(res));
+      }
+      {
+         RNTupleMerger merger{std::move(destinationChecksum)};
+         auto res = merger.Merge(sourcePtrs, opts);
+         EXPECT_TRUE(bool(res));
+      }
+      {
+         RNTupleMerger merger{std::move(destinationNoChecksum)};
+         auto res = merger.Merge(sourcePtrs, opts);
+         EXPECT_TRUE(bool(res));
+      }
+      {
+         opts.fCompressionSettings = 0;
+         RNTupleMerger merger{std::move(destinationUncomp)};
+         auto res = merger.Merge(sourcePtrs, opts);
+         EXPECT_TRUE(bool(res));
+      }
    }
 
    // Check that compression is the right one
@@ -940,18 +959,29 @@ TEST(RNTupleMerger, ChangeCompressionMixed)
       auto destinationUncomp = std::make_unique<RPageSinkFile>("ntuple", fileGuardOutUncomp.GetPath(), writeOpts);
       writeOpts.SetEnablePageChecksums(false);
 
-      RNTupleMerger merger;
       auto opts = RNTupleMergeOptions{};
-      auto res = merger.Merge(sourcePtrs, *destinationChecksum, opts);
-      EXPECT_TRUE(bool(res));
-      res = merger.Merge(sourcePtrs, *destinationNoChecksum, opts);
-      EXPECT_TRUE(bool(res));
-      opts.fCompressionSettings = 101;
-      res = merger.Merge(sourcePtrs, *destinationDifferentComp, opts);
-      EXPECT_TRUE(bool(res));
-      opts.fCompressionSettings = 0;
-      res = merger.Merge(sourcePtrs, *destinationUncomp, opts);
-      EXPECT_TRUE(bool(res));
+      {
+         RNTupleMerger merger{std::move(destinationChecksum)};
+         auto res = merger.Merge(sourcePtrs, opts);
+         EXPECT_TRUE(bool(res));
+      }
+      {
+         RNTupleMerger merger{std::move(destinationNoChecksum)};
+         auto res = merger.Merge(sourcePtrs, opts);
+         EXPECT_TRUE(bool(res));
+      }
+      {
+         opts.fCompressionSettings = 101;
+         RNTupleMerger merger{std::move(destinationDifferentComp)};
+         auto res = merger.Merge(sourcePtrs, opts);
+         EXPECT_TRUE(bool(res));
+      }
+      {
+         opts.fCompressionSettings = 0;
+         RNTupleMerger merger{std::move(destinationUncomp)};
+         auto res = merger.Merge(sourcePtrs, opts);
+         EXPECT_TRUE(bool(res));
+      }
    }
 
    // Check that compression is the right one
@@ -1015,11 +1045,11 @@ TEST(RNTupleMerger, MergeLateModelExtension)
       auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), wopts);
 
       // Now Merge the inputs
-      RNTupleMerger merger;
       auto opts = RNTupleMergeOptions{};
       opts.fCompressionSettings = 0;
       opts.fMergingMode = ENTupleMergingMode::kUnion;
-      auto res = merger.Merge(sourcePtrs, *destination, opts);
+      RNTupleMerger merger{std::move(destination)};
+      auto res = merger.Merge(sourcePtrs, opts);
       EXPECT_TRUE(bool(res));
    }
 
@@ -1094,7 +1124,6 @@ TEST(RNTupleMerger, MergeCompression)
       }
 
       // Now Merge the inputs
-      RNTupleMerger merger;
       RNTupleMergeOptions opts;
       {
          auto wopts = RNTupleWriteOptions();
@@ -1102,7 +1131,8 @@ TEST(RNTupleMerger, MergeCompression)
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), wopts);
          opts.fMergingMode = ENTupleMergingMode::kUnion;
          opts.fCompressionSettings = kOutCompSettings;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_TRUE(bool(res));
       }
    }
@@ -1169,14 +1199,14 @@ TEST(RNTupleMerger, DifferentCompatibleRepresentations)
       auto sourcePtrs2 = sourcePtrs;
 
       // Now Merge the inputs. Do both with and without compression change
-      RNTupleMerger merger;
       {
          auto wopts = RNTupleWriteOptions();
          wopts.SetCompression(0);
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), wopts);
          auto opts = RNTupleMergeOptions();
          opts.fCompressionSettings = 0;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          // TODO(gparolini): we want to support this in the future
          EXPECT_FALSE(bool(res));
          if (res.GetError()) {
@@ -1186,7 +1216,8 @@ TEST(RNTupleMerger, DifferentCompatibleRepresentations)
       }
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard4.GetPath(), RNTupleWriteOptions());
-         auto res = merger.Merge(sourcePtrs, *destination);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs);
          // TODO(gparolini): we want to support this in the future
          EXPECT_FALSE(bool(res));
          if (res.GetError()) {
@@ -1232,12 +1263,12 @@ TEST(RNTupleMerger, MultipleRepresentations)
 
       auto sourcePtrs2 = sourcePtrs;
 
-      RNTupleMerger merger;
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard2.GetPath(), RNTupleWriteOptions());
          auto opts = RNTupleMergeOptions();
          opts.fCompressionSettings = 0;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          // TODO(gparolini): we want to support this in the future
          // XXX: this currently fails because of a mismatch in the number of columns of dst vs src.
          // Is this correct? Anyway the situation will likely change once we properly support different representation
@@ -1291,14 +1322,14 @@ TEST(RNTupleMerger, Double32)
       auto sourcePtrs2 = sourcePtrs;
 
       // Now Merge the inputs. Do both with and without compression change
-      RNTupleMerger merger;
       {
          auto wopts = RNTupleWriteOptions();
          wopts.SetCompression(0);
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard3.GetPath(), wopts);
          auto opts = RNTupleMergeOptions();
          opts.fCompressionSettings = 0;
-         auto res = merger.Merge(sourcePtrs, *destination, opts);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs, opts);
          EXPECT_TRUE(bool(res));
       }
       {
@@ -1316,7 +1347,8 @@ TEST(RNTupleMerger, Double32)
       }
       {
          auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard4.GetPath(), RNTupleWriteOptions());
-         auto res = merger.Merge(sourcePtrs, *destination);
+         RNTupleMerger merger{std::move(destination)};
+         auto res = merger.Merge(sourcePtrs);
          EXPECT_TRUE(bool(res));
       }
       {
@@ -1365,8 +1397,8 @@ TEST(RNTupleMerger, MergeProjectedFields)
 
       // Now Merge the inputs
       auto destination = std::make_unique<RPageSinkFile>("ntuple", fileGuard2.GetPath(), RNTupleWriteOptions());
-      RNTupleMerger merger;
-      auto res = merger.Merge(sourcePtrs, *destination);
+      RNTupleMerger merger{std::move(destination)};
+      auto res = merger.Merge(sourcePtrs);
       EXPECT_TRUE(bool(res));
    }
 
diff --git a/tree/ntuple/v7/test/rfield_streamer.cxx b/tree/ntuple/v7/test/rfield_streamer.cxx
index 5b1b7d1ae917f..534b9aabbe0d6 100644
--- a/tree/ntuple/v7/test/rfield_streamer.cxx
+++ b/tree/ntuple/v7/test/rfield_streamer.cxx
@@ -193,8 +193,8 @@ TEST(RField, StreamerMerge)
       std::vector<RPageSource *> sourcePtrs{sources[0].get(), sources[1].get()};
       auto destination = std::make_unique<RPageSinkFile>("ntpl", fileGuard3.GetPath(), RNTupleWriteOptions());
 
-      RNTupleMerger merger;
-      EXPECT_NO_THROW(merger.Merge(sourcePtrs, *destination));
+      RNTupleMerger merger{std::move(destination)};
+      EXPECT_NO_THROW(merger.Merge(sourcePtrs));
    }
 
    auto reader = RNTupleReader::Open("ntpl", fileGuard3.GetPath());