diff --git a/src/github/operations/branch.ts b/src/github/operations/branch.ts
index aea1b9ce2..0896efa30 100644
--- a/src/github/operations/branch.ts
+++ b/src/github/operations/branch.ts
@@ -167,7 +167,13 @@ export async function setupBranch(
 
       // Execute git commands to checkout PR branch (dynamic depth based on PR size)
       // Using execFileSync instead of shell template literals for security
-      execGit(["fetch", "origin", `--depth=${fetchDepth}`, branchName]);
+      // Use GitHub's PR ref which works for both same-repo and fork PRs
+      execGit([
+        "fetch",
+        "origin",
+        `--depth=${fetchDepth}`,
+        `pull/${entityNumber}/head:${branchName}`,
+      ]);
       execGit(["checkout", branchName, "--"]);
 
       console.log(`Successfully checked out PR branch for PR #${entityNumber}`);