diff --git a/CHANGELOG.txt b/CHANGELOG.txt
index ffb7e10..209f055 100644
--- a/CHANGELOG.txt
+++ b/CHANGELOG.txt
@@ -13,6 +13,7 @@
 - use `StacBaseModel` as base model for `Asset` model (#148, @vincentsarago)
 - add `license` in `StacCommonMetadata` model (#147, @vincentsarago)
 - make `limit` optional in `api.Search` model (#150, @vincentsarago)
+- set `start/end datetime` to the datetime value when passing only one value in `api.Search` (#152, @vincentsarago)
 
 3.0.0 (2024-01-25)
 ------------------
diff --git a/stac_pydantic/api/search.py b/stac_pydantic/api/search.py
index c68fd60..57cfac0 100644
--- a/stac_pydantic/api/search.py
+++ b/stac_pydantic/api/search.py
@@ -108,9 +108,9 @@ def validate_datetime(cls, value: str) -> str:
                 "Invalid datetime range. Too many values. Must match format: {begin_date}/{end_date}"
             )
 
-        # If there is only one date, insert a None for the start date
+        # If there is only one date, duplicate to use for both start and end dates
         if len(values) == 1:
-            values.insert(0, None)
+            values = [values[0], values[0]]
 
         # Cast because pylance gets confused by the type adapter and annotated type
         dates = cast(
diff --git a/tests/api/test_search.py b/tests/api/test_search.py
index 95899ab..1615987 100644
--- a/tests/api/test_search.py
+++ b/tests/api/test_search.py
@@ -58,7 +58,7 @@ def test_temporal_search_single_tailed():
     utcnow = datetime.now(timezone.utc)
     utcnow_str = utcnow.isoformat()
     search = Search(collections=["collection1"], datetime=utcnow_str)
-    assert search.start_date is None
+    assert search.start_date == utcnow
     assert search.end_date == utcnow