diff --git a/test_runner/batch_others/test_wal_acceptor.py b/test_runner/batch_others/test_wal_acceptor.py
index e5351912fa..0177555787 100644
--- a/test_runner/batch_others/test_wal_acceptor.py
+++ b/test_runner/batch_others/test_wal_acceptor.py
@@ -344,7 +344,7 @@ class ProposerPostgres:
                 f"wal_acceptors = '{wal_acceptors}'\n",
             ])
 
-    def sync_safekeepers(self) -> str:
+    def sync_safekeepers(self, timeout=60) -> str:
         """
         Run 'postgres --sync-safekeepers'.
         Returns execution result, which is commit_lsn after sync.
@@ -355,7 +355,7 @@ class ProposerPostgres:
             "PGDATA": self.pg_data_dir_path(),
         }
 
-        basepath = self.pg_bin.run_capture(command, env)
+        basepath = self.pg_bin.run_capture(command, env, timeout=timeout)
         stdout_filename = basepath + '.stdout'
 
         with open(stdout_filename, 'r') as stdout_f:
@@ -438,3 +438,79 @@ def test_timeline_status(zenith_env_builder: ZenithEnvBuilder):
 
     epoch_after_reboot = wa_http_cli.timeline_status(tenant_id, timeline_id).acceptor_epoch
     assert epoch_after_reboot > epoch
+
+
+class WalAppender:
+    """Helper for appending WAL to safekeepers, keeps track of last inserted lsn."""
+
+    # 0/16B9188 is good lsn to start with, it's valid and not in the segment start, nor in zero segment
+    def __init__(self, acceptors, tenant_id, timeline_id, epoch_start_lsn=0x16B9188, begin_lsn=0x16B9188):
+        self.acceptors = acceptors
+        self.epoch_start_lsn = epoch_start_lsn
+        self.begin_lsn = begin_lsn
+        self.tenant_id = tenant_id
+        self.timeline_id = timeline_id
+        self.flush_lsns = dict()
+
+    def append(self, i, term, lm_message = "message", lm_prefix = "", set_commit_lsn = False):
+        """Append new logical message to i'th safekeeper."""
+        lsn = self.flush_lsns.get(i, self.begin_lsn)
+        req = {
+            "lm_prefix": lm_prefix,
+            "lm_message": lm_message,
+            "set_commit_lsn": set_commit_lsn,
+            "term": term,
+            "begin_lsn": lsn,
+            "epoch_start_lsn": self.epoch_start_lsn,
+            "truncate_lsn": self.begin_lsn,
+        }
+
+        res = self.acceptors[i].append_logical_message(
+            self.tenant_id,
+            self.timeline_id,
+            req,
+        )
+
+        end_lsn = res["inserted_wal"]["end_lsn"]
+        self.flush_lsns[i] = end_lsn
+
+        return res
+
+    def debug_print(self):
+        """Print lsn for each acceptor."""
+        for i, lsn in self.flush_lsns.items():
+            print(f'end_lsn for acceptors[{i}] = {lsn_to_hex(lsn)}')
+
+# one safekeeper with old term and a lot of non-commited wal
+def test_sync_safekeepers_old_term_ahead(repo_dir: str, pg_bin: PgBin, wa_factory: WalAcceptorFactory):
+    wa_factory.start_n_new(3)
+
+    timeline_id = uuid.uuid4().hex
+    tenant_id = uuid.uuid4().hex
+
+    # write config for proposer
+    pgdata_dir = os.path.join(repo_dir, "proposer_pgdata")
+    pg = ProposerPostgres(pgdata_dir, pg_bin, timeline_id, tenant_id)
+    pg.create_dir_config(wa_factory.get_connstrs())
+
+    # append wal to safekeepers
+    appender = WalAppender(wa_factory.instances, tenant_id, timeline_id)
+
+    appender.append(0, term=1, lm_message="msg1")
+    appender.append(1, term=1, lm_message="msg1")
+    appender.append(2, term=1, lm_message="msg1")
+
+    appender.append(2, term=1, lm_message="msg1")
+    appender.append(2, term=1, lm_message="msg1")
+    appender.append(2, term=1, lm_message="msg1")
+    appender.append(2, term=1, lm_message="msg1")
+
+    appender.append(0, term=2, lm_message="msg2")
+    appender.append(1, term=2, lm_message="msg2")
+
+    # run sync safekeepers
+    # FIXME: fails with timeout
+    lsn_after_sync = pg.sync_safekeepers()
+    print(f"lsn after sync = {lsn_after_sync}")
+
+    appender.debug_print()
diff --git a/vendor/postgres b/vendor/postgres
index a97cfe8ed7..56c561aa77 160000
--- a/vendor/postgres
+++ b/vendor/postgres
@@ -1 +1 @@
-Subproject commit a97cfe8ed781857b2880bf1e0b4ff04972b9c8dc
+Subproject commit 56c561aa770b01d9e5cfcbf064eebe33349b7f77