diff --git a/src/Elastic.Documentation.OpenApiIndex/VersionIndexBuilder.cs b/src/Elastic.Documentation.OpenApiIndex/VersionIndexBuilder.cs
index d6a4125f00..6e4631e4b6 100644
--- a/src/Elastic.Documentation.OpenApiIndex/VersionIndexBuilder.cs
+++ b/src/Elastic.Documentation.OpenApiIndex/VersionIndexBuilder.cs
@@ -10,7 +10,9 @@ namespace Elastic.Documentation.OpenApiIndex;
 /// Builds a <see cref="RootVersionIndex"/> from the object keys in the <c>elastic-docs-openapi-specs</c>
 /// bucket, keeping the highest minor published for each major. Keys are expected in the shape written by
 /// <c>elastic/docs-actions/openapi/upload</c>: <c>{org}/{repo}/{version}/{fileName}</c>, where
-/// <c>version</c> is either <c>main</c> or a validated <c>{major}.{minor}</c> release version.
+/// <c>version</c> is the publishing branch: <c>main</c>, <c>master</c>, or a validated
+/// <c>{major}.{minor}</c> release version. <c>master</c> indexes under the <c>main</c> moniker so
+/// a repo keeps its real branch name in the object key without every workflow overriding it.
 /// </summary>
 public static class VersionIndexBuilder
 {
@@ -69,10 +71,12 @@ private static bool TryParseKey(string key, out string repo, out string version,
 	/// <summary>Resolves the index key ("main", or the major number) and a sortable minor for a version segment.</summary>
 	private static bool TryParseVersion(string version, out string major, out int minor)
 	{
-		if (version == "main")
+		// Both default-branch names share the "main" key. If a repo somehow publishes from both,
+		// the higher minor wins like any other collision, so main beats master.
+		if (version is "main" or "master")
 		{
 			major = "main";
-			minor = 0;
+			minor = version == "main" ? 1 : 0;
 			return true;
 		}
 
diff --git a/tests/Elastic.Documentation.OpenApiIndex.Tests/VersionIndexBuilderTests.cs b/tests/Elastic.Documentation.OpenApiIndex.Tests/VersionIndexBuilderTests.cs
index e053aa2fb2..7ff88991b3 100644
--- a/tests/Elastic.Documentation.OpenApiIndex.Tests/VersionIndexBuilderTests.cs
+++ b/tests/Elastic.Documentation.OpenApiIndex.Tests/VersionIndexBuilderTests.cs
@@ -52,6 +52,26 @@ public void Build_MainVersion_CreatesMainEntry()
 		index["elastic/elasticsearch"]["openapi.json"]["main"].Version.Should().Be("main");
 	}
 
+	[Fact]
+	public void Build_MasterVersion_IndexesUnderMainWithMasterObjectKey()
+	{
+		var index = VersionIndexBuilder.Build(["elastic/cloud/master/cloud.json"]).Index;
+
+		var byMajor = index["elastic/cloud"]["cloud.json"];
+		byMajor.Should().ContainSingle().Which.Key.Should().Be("main");
+		byMajor["main"].Version.Should().Be("master");
+	}
+
+	[Fact]
+	public void Build_MainAndMasterBothPublished_MainWins()
+	{
+		var index = VersionIndexBuilder.Build(["elastic/cloud/master/cloud.json", "elastic/cloud/main/cloud.json"]).Index;
+
+		var byMajor = index["elastic/cloud"]["cloud.json"];
+		byMajor.Should().ContainSingle().Which.Key.Should().Be("main");
+		byMajor["main"].Version.Should().Be("main");
+	}
+
 	[Fact]
 	public void Build_MainAndReleaseVersions_KeepsBothSeparately()
 	{
@@ -97,7 +117,7 @@ public void Build_MultipleRepos_KeepsSeparateEntriesPerRepo()
 
 	[InlineData("elastic/elasticsearch/8.16/")] // empty file segment
 
-	[InlineData("elastic/elasticsearch/master/openapi.json")] // not "main" or <major>.<minor>
+	[InlineData("elastic/elasticsearch/not-a-branch/openapi.json")] // not main, master, or <major>.<minor>
 
 	[InlineData("elastic/elasticsearch/8/openapi.json")] // missing minor
 
@@ -123,10 +143,10 @@ public void Build_MixOfValidAndInvalidKeys_IndexesValidAndReportsInvalidOnly()
 		var (index, invalidKeys) = VersionIndexBuilder.Build([
 			"elastic/elasticsearch/8.16/openapi.json",
 			"not-a-valid-key",
-			"elastic/elasticsearch/master/openapi.json"
+			"elastic/elasticsearch/not-a-branch/openapi.json"
 		]);
 
 		index["elastic/elasticsearch"]["openapi.json"]["8"].Version.Should().Be("8.16");
-		invalidKeys.Should().BeEquivalentTo(["not-a-valid-key", "elastic/elasticsearch/master/openapi.json"]);
+		invalidKeys.Should().BeEquivalentTo(["not-a-valid-key", "elastic/elasticsearch/not-a-branch/openapi.json"]);
 	}
 }