diff --git a/eng/pipelines/runtime-official.yml b/eng/pipelines/runtime-official.yml
index be2359ae1e66b6..906798926b8389 100644
--- a/eng/pipelines/runtime-official.yml
+++ b/eng/pipelines/runtime-official.yml
@@ -54,9 +54,10 @@ stages:
   #
   # Source Index Build
   #
-  - template: /eng/common/templates/job/source-index-stage1.yml
-    parameters:
-      sourceIndexBuildCommand: build.cmd -subset libs.ref+libs.src -binarylog -os Linux -ci
+  - ${{ if eq(variables['Build.SourceBranch'], 'refs/heads/main') }}:
+    - template: /eng/common/templates/job/source-index-stage1.yml
+      parameters:
+        sourceIndexBuildCommand: build.cmd -subset libs.ref+libs.src -binarylog -os Linux -ci
 
   #
   # Build CoreCLR