diff --git a/navi/core/sqlite_session_store.py b/navi/core/sqlite_session_store.py
index 8583c53..e8ce93f 100644
--- a/navi/core/sqlite_session_store.py
+++ b/navi/core/sqlite_session_store.py
@@ -30,6 +30,14 @@
     )
 
 
+def _parse_dt(value: str) -> datetime:
+    """Parse ISO datetime string, always returning a timezone-aware datetime."""
+    dt = datetime.fromisoformat(value)
+    if dt.tzinfo is None:
+        dt = dt.replace(tzinfo=timezone.utc)
+    return dt
+
+
 def _deserialize(raw: str) -> list[Message]:
     if not raw:
         return []
@@ -119,6 +127,6 @@
             messages=messages,
             context=context,
             pinned=bool(pinned),
-            created_at=datetime.fromisoformat(created_at),
-            last_active=datetime.fromisoformat(last_active),
+            created_at=_parse_dt(created_at),
+            last_active=_parse_dt(last_active),
         )