diff --git a/test_runner/batch_others/test_timeline_size.py b/test_runner/batch_others/test_timeline_size.py
index c736893f99..6e1168e38f 100644
--- a/test_runner/batch_others/test_timeline_size.py
+++ b/test_runner/batch_others/test_timeline_size.py
@@ -4,7 +4,7 @@ from uuid import UUID
 import re
 import psycopg2.extras
 import psycopg2.errors
-from fixtures.neon_fixtures import NeonEnv, NeonEnvBuilder, Postgres, assert_timeline_local
+from fixtures.neon_fixtures import NeonEnv, NeonEnvBuilder, Postgres, assert_timeline_local, wait_for_last_flush_lsn
 from fixtures.log_helper import log
 import time
 
@@ -192,6 +192,8 @@ def test_timeline_physical_size_init(neon_simple_env: NeonEnv):
            FROM generate_series(1, 1000) g""",
     ])
 
+    wait_for_last_flush_lsn(env, pg, env.initial_tenant, new_timeline_id)
+
     # restart the pageserer to force calculating timeline's initial physical size
     env.pageserver.stop()
     env.pageserver.start()
@@ -211,7 +213,9 @@ def test_timeline_physical_size_post_checkpoint(neon_simple_env: NeonEnv):
            FROM generate_series(1, 1000) g""",
     ])
 
+    wait_for_last_flush_lsn(env, pg, env.initial_tenant, new_timeline_id)
     env.pageserver.safe_psql(f"checkpoint {env.initial_tenant.hex} {new_timeline_id.hex}")
+
     assert_physical_size(env, env.initial_tenant, new_timeline_id)
 
 
@@ -232,8 +236,10 @@ def test_timeline_physical_size_post_compaction(neon_env_builder: NeonEnvBuilder
            FROM generate_series(1, 100000) g""",
     ])
 
+    wait_for_last_flush_lsn(env, pg, env.initial_tenant, new_timeline_id)
     env.pageserver.safe_psql(f"checkpoint {env.initial_tenant.hex} {new_timeline_id.hex}")
     env.pageserver.safe_psql(f"compact {env.initial_tenant.hex} {new_timeline_id.hex}")
+
     assert_physical_size(env, env.initial_tenant, new_timeline_id)
 
 
@@ -254,15 +260,21 @@ def test_timeline_physical_size_post_gc(neon_env_builder: NeonEnvBuilder):
            SELECT 'long string to consume some space' || g
            FROM generate_series(1, 100000) g""",
     ])
+
+    wait_for_last_flush_lsn(env, pg, env.initial_tenant, new_timeline_id)
     env.pageserver.safe_psql(f"checkpoint {env.initial_tenant.hex} {new_timeline_id.hex}")
+
     pg.safe_psql("""
         INSERT INTO foo
             SELECT 'long string to consume some space' || g
             FROM generate_series(1, 100000) g
     """)
+
+    wait_for_last_flush_lsn(env, pg, env.initial_tenant, new_timeline_id)
     env.pageserver.safe_psql(f"checkpoint {env.initial_tenant.hex} {new_timeline_id.hex}")
 
     env.pageserver.safe_psql(f"do_gc {env.initial_tenant.hex} {new_timeline_id.hex} 0")
+
     assert_physical_size(env, env.initial_tenant, new_timeline_id)
 
 
@@ -279,6 +291,7 @@ def test_timeline_physical_size_metric(neon_simple_env: NeonEnv):
            FROM generate_series(1, 100000) g""",
     ])
 
+    wait_for_last_flush_lsn(env, pg, env.initial_tenant, new_timeline_id)
     env.pageserver.safe_psql(f"checkpoint {env.initial_tenant.hex} {new_timeline_id.hex}")
 
     # get the metrics and parse the metric for the current timeline's physical size
@@ -319,6 +332,7 @@ def test_tenant_physical_size(neon_simple_env: NeonEnv):
             f"INSERT INTO foo SELECT 'long string to consume some space' || g FROM generate_series(1, {n_rows}) g",
         ])
 
+        wait_for_last_flush_lsn(env, pg, tenant, timeline)
         env.pageserver.safe_psql(f"checkpoint {tenant.hex} {timeline.hex}")
 
         timeline_total_size += get_timeline_physical_size(timeline)
diff --git a/test_runner/fixtures/neon_fixtures.py b/test_runner/fixtures/neon_fixtures.py
index 3b87f290b8..d5b0af3813 100644
--- a/test_runner/fixtures/neon_fixtures.py
+++ b/test_runner/fixtures/neon_fixtures.py
@@ -2475,3 +2475,9 @@ def wait_for_last_record_lsn(pageserver_http_client: NeonPageserverHttpClient,
         time.sleep(1)
     raise Exception("timed out while waiting for last_record_lsn to reach {}, was {}".format(
         lsn_to_hex(lsn), lsn_to_hex(current_lsn)))
+
+
+def wait_for_last_flush_lsn(env: NeonEnv, pg: Postgres, tenant: uuid.UUID, timeline: uuid.UUID):
+    """Wait for pageserver to catch up the latest flush LSN"""
+    last_flush_lsn = lsn_from_hex(pg.safe_psql("SELECT pg_current_wal_flush_lsn()")[0][0])
+    wait_for_last_record_lsn(env.pageserver.http_client(), tenant, timeline, last_flush_lsn)