diff --git a/scripts/github/update/open/pr.sh b/scripts/github/update/open/pr.sh
index f093369356..83edcfd089 100755
--- a/scripts/github/update/open/pr.sh
+++ b/scripts/github/update/open/pr.sh
@@ -79,6 +79,11 @@ for entry in "${OPEN_PRS[@]}"; do
 	[[ -z "${entry}" ]] && continue
 	pr_num="${entry%%$'\t'*}"
 	pr_branch="${entry##*$'\t'}"
+	if [[ "${pr_branch}" == *"-${LOCAL_FP:0:7}" ]]; then
+		echo "  open PR #${pr_num} (${pr_branch}): branch name carries this fingerprint"
+		DUPLICATE_PR="${pr_num}"
+		break
+	fi
 	pr_head="$(gh pr view "${pr_num}" --repo "${REPO}" --json headRefOid --jq .headRefOid 2>/dev/null || true)"
 	if [[ -z "${pr_head}" ]] || ! git fetch --quiet --depth 1 origin "${pr_head}" 2>/dev/null; then
 		echo "  open PR #${pr_num} (${pr_branch}): head unfetchable; treating as non-duplicate"
diff --git a/tests/unit/python/scripts/github/update/__init__.py b/tests/unit/python/scripts/github/update/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/unit/python/scripts/github/update/open/__init__.py b/tests/unit/python/scripts/github/update/open/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/unit/python/scripts/github/update/open/test_pr.py b/tests/unit/python/scripts/github/update/open/test_pr.py
new file mode 100644
index 0000000000..6729c3e1e5
--- /dev/null
+++ b/tests/unit/python/scripts/github/update/open/test_pr.py
@@ -0,0 +1,112 @@
+from __future__ import annotations
+
+import os
+import subprocess
+import tempfile
+import unittest
+from pathlib import Path
+
+from utils.cache.files import PROJECT_ROOT
+
+SCRIPT = PROJECT_ROOT / "scripts" / "github" / "update" / "open" / "pr.sh"
+PINNED_FILE = "pin.txt"
+GH_STUB = """#!/usr/bin/env bash
+if [[ "$1 $2" == "pr list" ]]; then
+	printf '7\\t%s\\n' "${GH_STUB_BRANCH}"
+fi
+"""
+
+
+class UpdatePrFixture:
+    """A throwaway repo with one pending pin bump and a ``gh`` that lists one open PR.
+
+    Args:
+        tmp: directory that holds the repo and the ``gh`` stub.
+    """
+
+    def __init__(self, tmp: str) -> None:
+        self.repo = Path(tmp) / "repo"
+        self.repo.mkdir()
+        stub_dir = Path(tmp) / "bin"
+        stub_dir.mkdir()
+        stub = stub_dir / "gh"
+        stub.write_text(GH_STUB)
+        stub.chmod(0o755)
+        inherited = {k: v for k, v in os.environ.items() if not k.startswith("GIT_")}
+        self.env = {
+            **inherited,
+            "PATH": f"{stub_dir}{os.pathsep}{os.environ['PATH']}",
+            "GIT_CONFIG_GLOBAL": os.devnull,
+            "GIT_ALLOW_PROTOCOL": "file",
+            "GH_TOKEN": "unused",
+            "UPDATE_BRANCH_PREFIX": "update/pins",
+            "UPDATE_BRANCH_SUFFIX": "20260101",
+            "UPDATE_BASE_BRANCH": "main",
+            "UPDATE_COMMIT_MESSAGE": "update: bump",
+            "UPDATE_PR_TITLE": "update: bump",
+            "UPDATE_PR_BODY": "bump",
+        }
+        self.git("init", "-b", "main")
+        self.git("remote", "add", "origin", "https://github.com/acme/widgets.git")
+        (self.repo / PINNED_FILE).write_text("1.0\n")
+        self.git("add", "-A")
+        self.git(
+            "-c",
+            "user.name=test",
+            "-c",
+            "user.email=test@example.invalid",
+            "commit",
+            "-m",
+            "init",
+        )
+        (self.repo / PINNED_FILE).write_text("1.1\n")
+
+    def git(self, *args: str, stdin: str | None = None) -> str:
+        return subprocess.run(
+            ["git", *args],
+            cwd=self.repo,
+            env=self.env,
+            input=stdin,
+            capture_output=True,
+            text=True,
+            check=True,
+        ).stdout.strip()
+
+    def fingerprint(self) -> str:
+        blob = self.git("hash-object", PINNED_FILE)
+        return self.git("hash-object", "--stdin", stdin=f"{blob}\t{PINNED_FILE}\n")
+
+    def open_pr(self, open_branch: str) -> subprocess.CompletedProcess:
+        return subprocess.run(
+            ["bash", str(SCRIPT)],
+            cwd=self.repo,
+            env={**self.env, "GH_STUB_BRANCH": open_branch},
+            capture_output=True,
+            text=True,
+            check=False,
+        )
+
+
+class TestUpdatePrDedupe(unittest.TestCase):
+    def test_edited_branch_of_the_same_proposal_is_a_duplicate(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            fixture = UpdatePrFixture(tmp)
+            branch = f"update/pins-20251231-{fixture.fingerprint()[:7]}"
+            result = fixture.open_pr(branch)
+            self.assertEqual(result.returncode, 0, result.stdout + result.stderr)
+            self.assertIn("Open PR #7 already carries this exact change", result.stdout)
+            self.assertNotIn("Pushing change to branch", result.stdout)
+
+    def test_branch_of_another_proposal_is_not_a_duplicate(self) -> None:
+        with tempfile.TemporaryDirectory() as tmp:
+            fixture = UpdatePrFixture(tmp)
+            result = fixture.open_pr("update/pins-20251231-0000000")
+            self.assertNotIn("already carries this exact change", result.stdout)
+            self.assertIn(
+                f"Pushing change to branch update/pins-20260101-{fixture.fingerprint()[:7]}",
+                result.stdout,
+            )
+
+
+if __name__ == "__main__":
+    unittest.main()