diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3f683f94..a11d0722 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -28,6 +28,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Fixed
 
+- Allow additional top-level properties on collections [#191](https://github.com/stac-utils/stac-fastapi-elasticsearch-opensearch/pull/191)
 - Exclude unset fields in search response [#166](https://github.com/stac-utils/stac-fastapi-elasticsearch/issues/166)
 - Upgrade stac-fastapi to v2.4.9 [#172](https://github.com/stac-utils/stac-fastapi-elasticsearch/pull/172)
 - Set correct default filter-lang for GET /search requests [#179](https://github.com/stac-utils/stac-fastapi-elasticsearch/issues/179)
diff --git a/stac_fastapi/elasticsearch/stac_fastapi/elasticsearch/serializers.py b/stac_fastapi/elasticsearch/stac_fastapi/elasticsearch/serializers.py
index 725e8f65..ee53320b 100644
--- a/stac_fastapi/elasticsearch/stac_fastapi/elasticsearch/serializers.py
+++ b/stac_fastapi/elasticsearch/stac_fastapi/elasticsearch/serializers.py
@@ -1,5 +1,6 @@
 """Serializers."""
 import abc
+from copy import deepcopy
 from typing import Any
 
 import attr
@@ -121,18 +122,24 @@ def db_to_stac(cls, collection: dict, base_url: str) -> stac_types.Collection:
         Returns:
             stac_types.Collection: The STAC collection object.
         """
-        # Use dictionary unpacking to extract values from the collection dictionary
+        # Avoid modifying the input dict in-place ... doing so breaks some tests
+        collection = deepcopy(collection)
+
+        # Set defaults
         collection_id = collection.get("id")
-        stac_extensions = collection.get("stac_extensions", [])
-        stac_version = collection.get("stac_version", "")
-        title = collection.get("title", "")
-        description = collection.get("description", "")
-        keywords = collection.get("keywords", [])
-        license = collection.get("license", "")
-        providers = collection.get("providers", {})
-        summaries = collection.get("summaries", {})
-        extent = collection.get("extent", {})
-        collection_assets = collection.get("assets", {})
+        collection.setdefault("type", "Collection")
+        collection.setdefault("stac_extensions", [])
+        collection.setdefault("stac_version", "")
+        collection.setdefault("title", "")
+        collection.setdefault("description", "")
+        collection.setdefault("keywords", [])
+        collection.setdefault("license", "")
+        collection.setdefault("providers", [])
+        collection.setdefault("summaries", {})
+        collection.setdefault(
+            "extent", {"spatial": {"bbox": []}, "temporal": {"interval": []}}
+        )
+        collection.setdefault("assets", {})
 
         # Create the collection links using CollectionLinks
         collection_links = CollectionLinks(
@@ -143,20 +150,7 @@ def db_to_stac(cls, collection: dict, base_url: str) -> stac_types.Collection:
         original_links = collection.get("links")
         if original_links:
             collection_links += resolve_links(original_links, base_url)
+        collection["links"] = collection_links
 
         # Return the stac_types.Collection object
-        return stac_types.Collection(
-            type="Collection",
-            id=collection_id,
-            stac_extensions=stac_extensions,
-            stac_version=stac_version,
-            title=title,
-            description=description,
-            keywords=keywords,
-            license=license,
-            providers=providers,
-            summaries=summaries,
-            extent=extent,
-            links=collection_links,
-            assets=collection_assets,
-        )
+        return stac_types.Collection(**collection)
diff --git a/stac_fastapi/elasticsearch/tests/resources/test_collection.py b/stac_fastapi/elasticsearch/tests/resources/test_collection.py
index 9061ac1e..dbd88da2 100644
--- a/stac_fastapi/elasticsearch/tests/resources/test_collection.py
+++ b/stac_fastapi/elasticsearch/tests/resources/test_collection.py
@@ -5,6 +5,22 @@
 
 from ..conftest import create_collection, delete_collections_and_items, refresh_indices
 
+CORE_COLLECTION_PROPS = [
+    "id",
+    "type",
+    "stac_extensions",
+    "stac_version",
+    "title",
+    "description",
+    "keywords",
+    "license",
+    "providers",
+    "summaries",
+    "extent",
+    "links",
+    "assets",
+]
+
 
 @pytest.mark.asyncio
 async def test_create_and_delete_collection(app_client, load_test_data):
@@ -84,6 +100,32 @@ async def test_returns_valid_collection(ctx, app_client):
     collection.validate()
 
 
+@pytest.mark.asyncio
+async def test_collection_extensions(ctx, app_client):
+    """Test that extensions can be used to define additional top-level properties"""
+    ctx.collection.get("stac_extensions", []).append(
+        "https://stac-extensions.github.io/item-assets/v1.0.0/schema.json"
+    )
+    test_asset = {"title": "test", "description": "test", "type": "test"}
+    ctx.collection["item_assets"] = {"test": test_asset}
+    resp = await app_client.put("/collections", json=ctx.collection)
+
+    assert resp.status_code == 200
+    assert resp.json().get("item_assets", {}).get("test") == test_asset
+
+
+@pytest.mark.asyncio
+async def test_collection_defaults(app_client):
+    """Test that properties omitted by client are populated w/ default values"""
+    minimal_coll = {"id": str(uuid.uuid4())}
+    resp = await app_client.post("/collections", json=minimal_coll)
+
+    assert resp.status_code == 200
+    resp_json = resp.json()
+    for prop in CORE_COLLECTION_PROPS:
+        assert prop in resp_json.keys()
+
+
 @pytest.mark.asyncio
 async def test_pagination_collection(app_client, ctx, txn_client):
     """Test collection pagination links"""