diff --git a/actions/setup/js/update_pull_request.cjs b/actions/setup/js/update_pull_request.cjs
index a80344b526d..dcdca3b020e 100644
--- a/actions/setup/js/update_pull_request.cjs
+++ b/actions/setup/js/update_pull_request.cjs
@@ -38,6 +38,7 @@ function isNonFatalUpdateBranchError(error) {
   // Require both permission wording and update-branch context to avoid treating unrelated
   // "workflows permission" errors as non-fatal for pull request branch updates.
   const hasWorkflowsPermissionError = hasWorkflowsPermissionPhrase && (hasWorkflowMutationRefusal || message.includes("update pull request"));
+  const hasVerifiedSignaturesRuleViolation = message.includes("repository rule violations found") && /commits?\s+must\s+have\s+verified\s+signatures\b/i.test(message);
 
   if (status !== undefined) {
     if (status === 403 && hasWorkflowsPermissionError) {
@@ -51,8 +52,10 @@ function isNonFatalUpdateBranchError(error) {
   // GitHub update-branch API can return these 422 messages for benign conditions:
   // - already up to date ("There are no new commits on the base branch")
   // - cannot auto-update due to conflict ("merge conflict between base and head")
+  // - branch protection/ruleset refusal when the synthetic merge commit would be unsigned
+  //   ("Repository rule violations found" + "Commits must have verified signatures")
   // These should not fail safe output processing.
-  return message.includes("there are no new commits on the base branch") || message.includes("merge conflict between base and head") || hasWorkflowsPermissionError;
+  return message.includes("there are no new commits on the base branch") || message.includes("merge conflict between base and head") || hasWorkflowsPermissionError || hasVerifiedSignaturesRuleViolation;
 }
 
 /**
diff --git a/actions/setup/js/update_pull_request.test.cjs b/actions/setup/js/update_pull_request.test.cjs
index 6fb5e16ae11..7f2ad8f7cd8 100644
--- a/actions/setup/js/update_pull_request.test.cjs
+++ b/actions/setup/js/update_pull_request.test.cjs
@@ -941,4 +941,40 @@ describe("update_pull_request.cjs - update_branch behavior", () => {
     });
     expect(mockCore.warning).toHaveBeenCalledWith(expect.stringContaining("branch from base (non-fatal)"));
   });
+
+  it("should treat verified-signatures ruleset rejection as non-fatal for update-branch-only requests", async () => {
+    const ruleViolationError = new Error("Repository rule violations found\n\nCommits must have verified signatures.");
+    ruleViolationError.status = 422;
+    mockGithub.rest.pulls.updateBranch.mockRejectedValueOnce(ruleViolationError);
+
+    const handler = await updatePRModule.main({ update_branch: true });
+    const result = await handler({ pull_request_number: 100 });
+
+    expect(result.success).toBe(true);
+    expect(mockGithub.rest.pulls.updateBranch).toHaveBeenCalledTimes(1);
+    expect(mockGithub.rest.pulls.update).not.toHaveBeenCalled();
+    expect(mockCore.warning).toHaveBeenCalledWith(expect.stringContaining("branch from base (non-fatal)"));
+  });
+
+  it("should continue title/body updates when updateBranch hits verified-signatures ruleset rejection", async () => {
+    const ruleViolationError = new Error("Repository rule violations found\n\nCommits must have verified signatures.");
+    ruleViolationError.status = 422;
+    mockGithub.rest.pulls.updateBranch.mockRejectedValueOnce(ruleViolationError);
+
+    const handler = await updatePRModule.main({ update_branch: true });
+    const result = await handler({
+      pull_request_number: 100,
+      title: "Updated PR",
+    });
+
+    expect(result.success).toBe(true);
+    expect(mockGithub.rest.pulls.updateBranch).toHaveBeenCalledTimes(1);
+    expect(mockGithub.rest.pulls.update).toHaveBeenCalledWith({
+      owner: "testowner",
+      repo: "testrepo",
+      pull_number: 100,
+      title: "Updated PR",
+    });
+    expect(mockCore.warning).toHaveBeenCalledWith(expect.stringContaining("branch from base (non-fatal)"));
+  });
 });