diff --git a/src/services/Elastic.Changelog/Evaluation/ChangelogPrepareArtifactService.cs b/src/services/Elastic.Changelog/Evaluation/ChangelogPrepareArtifactService.cs
index a7b768073e..4308bf1e2c 100644
--- a/src/services/Elastic.Changelog/Evaluation/ChangelogPrepareArtifactService.cs
+++ b/src/services/Elastic.Changelog/Evaluation/ChangelogPrepareArtifactService.cs
@@ -47,11 +47,17 @@ public async Task<bool> PrepareArtifact(IDiagnosticsCollector collector, Prepare
 
 			if (sourceYaml != null)
 			{
-				changelogFilename = input.ExistingChangelogFilename != null
-					? _fileSystem.Path.GetFileName(input.ExistingChangelogFilename)
+				// Treat empty as unset: CLI parsers (e.g. Argh) forward `--flag ""`
+				// as the empty string instead of null. An empty filename here would
+				// make Path.Combine(OutputDir, "") collapse to OutputDir itself and
+				// turn the artifact write into a write against the directory path,
+				// which fails with EACCES on Linux.
+				var hasExistingFilename = !string.IsNullOrEmpty(input.ExistingChangelogFilename);
+				changelogFilename = hasExistingFilename
+					? _fileSystem.Path.GetFileName(input.ExistingChangelogFilename!)
 					: _fileSystem.Path.GetFileName(sourceYaml);
 
-				if (input.ExistingChangelogFilename != null)
+				if (hasExistingFilename)
 					_logger.LogInformation("Reusing existing filename {Filename} for stable path on branch", changelogFilename);
 
 				var destYaml = _fileSystem.Path.Combine(input.OutputDir, changelogFilename);
diff --git a/tests/Elastic.Changelog.Tests/Evaluation/ChangelogPrepareArtifactServiceTests.cs b/tests/Elastic.Changelog.Tests/Evaluation/ChangelogPrepareArtifactServiceTests.cs
index 6e8450bba0..b084a2208a 100644
--- a/tests/Elastic.Changelog.Tests/Evaluation/ChangelogPrepareArtifactServiceTests.cs
+++ b/tests/Elastic.Changelog.Tests/Evaluation/ChangelogPrepareArtifactServiceTests.cs
@@ -232,6 +232,26 @@ public async Task PrepareArtifact_ExistingFilename_RenamesStagingFileToMatch()
 		metadata.ChangelogFilename.Should().Be("1735689600-old-title.yaml");
 	}
 
+	[Fact]
+	public async Task PrepareArtifact_EmptyExistingFilename_FallsBackToStagingFilename()
+	{
+		// Regression: CLI parsers (Argh) forward `--existing-changelog-filename ""`
+		// as the empty string instead of null. An empty filename used to make
+		// Path.Combine(OutputDir, "") collapse to OutputDir itself and write the
+		// artifact YAML at the directory path → EACCES on Linux.
+		await SetupStagingYaml("1735700000-new-title.yaml");
+		await SetupConfig();
+		var service = CreateService();
+		var args = DefaultArgs() with { ExistingChangelogFilename = string.Empty };
+
+		var result = await service.PrepareArtifact(Collector, args, CancellationToken.None);
+
+		result.Should().BeTrue();
+		FileSystem.File.Exists(Path.Join(OutputDir, "1735700000-new-title.yaml")).Should().BeTrue();
+		var metadata = ReadMetadata();
+		metadata.ChangelogFilename.Should().Be("1735700000-new-title.yaml");
+	}
+
 	[Fact]
 	public async Task PrepareArtifact_MissingStagingYaml_StatusError()
 	{