diff --git a/yente/search/base.py b/yente/search/base.py
index 87344899..ae7fc5d0 100644
--- a/yente/search/base.py
+++ b/yente/search/base.py
@@ -1,6 +1,7 @@
 import time
 import asyncio
 import warnings
+from threading import Lock
 from typing import cast, Any, Dict
 from structlog.contextvars import get_contextvars
 from elasticsearch import AsyncElasticsearch
@@ -15,7 +16,7 @@
 log = get_logger(__name__)
 POOL: Dict[int, AsyncElasticsearch] = {}
 query_semaphore = asyncio.Semaphore(settings.QUERY_CONCURRENCY)
-index_semaphore = asyncio.Semaphore(settings.INDEX_CONCURRENCY)
+index_lock = Lock()
 
 
 def get_opaque_id() -> str:
diff --git a/yente/search/indexer.py b/yente/search/indexer.py
index 6b21025f..cd2b9fa3 100644
--- a/yente/search/indexer.py
+++ b/yente/search/indexer.py
@@ -14,7 +14,7 @@
 from yente.data.dataset import Dataset
 from yente.data import get_catalog
 from yente.data.loader import load_json_lines
-from yente.search.base import get_es, close_es, index_semaphore
+from yente.search.base import get_es, close_es, index_lock
 from yente.search.mapping import make_entity_mapping
 from yente.search.mapping import INDEX_SETTINGS
 from yente.search.mapping import NAMES_FIELD, NAME_PHONETIC_FIELD
@@ -66,7 +66,10 @@ async def iter_entity_docs(
 async def index_entities_rate_limit(
     es: AsyncElasticsearch, dataset: Dataset, force: bool
 ) -> bool:
-    async with index_semaphore:
+    if index_lock.locked():
+        log.info("Index is already being updated", dataset=dataset.name, force=force)
+        return False
+    with index_lock:
         return await index_entities(es, dataset, force=force)
 
 
@@ -174,11 +177,9 @@ async def update_index(force: bool = False) -> bool:
     try:
         catalog = await get_catalog()
         log.info("Index update check")
-        indexers = []
+        changed = False
         for dataset in catalog.datasets:
-            indexers.append(index_entities_rate_limit(es, dataset, force))
-        results = await asyncio.gather(*indexers)
-        changed = True in results
+            changed = changed or await index_entities_rate_limit(es, dataset, force)
         log.info("Index update complete.", changed=changed)
         return changed
     finally:
diff --git a/yente/settings.py b/yente/settings.py
index 6c70e1d1..05fa717f 100644
--- a/yente/settings.py
+++ b/yente/settings.py
@@ -136,9 +136,6 @@ def env_str(name: str, default: str) -> str:
 # How many match and search queries to run against ES in parallel:
 QUERY_CONCURRENCY = int(env_str("YENTE_QUERY_CONCURRENCY", "10"))
 
-# How many index operations to run against ES in parallel:
-INDEX_CONCURRENCY = int(env_str("YENTE_INDEX_CONCURRENCY", "5"))
-
 # Default scoring threshold for /match results:
 SCORE_THRESHOLD = 0.70