diff --git a/backend/onyx/db/entities.py b/backend/onyx/db/entities.py
index 9696ce9267..ade11bfd51 100644
--- a/backend/onyx/db/entities.py
+++ b/backend/onyx/db/entities.py
@@ -12,6 +12,7 @@
 from sqlalchemy.orm import Session
 
 import onyx.db.document as dbdocument
+from onyx.db.entity_type import UNGROUNDED_SOURCE_NAME
 from onyx.db.models import Document
 from onyx.db.models import KGEntity
 from onyx.db.models import KGEntityExtractionStaging
@@ -328,7 +329,13 @@ def get_entity_stats_by_grounded_source_name(
         .group_by(KGEntityType.grounded_source_name)
         .all()
     )
+
+    # `row.grounded_source_name` is NULLABLE in the database schema.
+    # Thus, for all "ungrounded" entity-types, we use a default name.
     return {
-        row.grounded_source_name: (row.last_updated, row.entities_count)
+        (row.grounded_source_name or UNGROUNDED_SOURCE_NAME): (
+            row.last_updated,
+            row.entities_count,
+        )
         for row in results
     }
diff --git a/backend/onyx/db/entity_type.py b/backend/onyx/db/entity_type.py
index 54b7bfaff3..a88ac9c2ac 100644
--- a/backend/onyx/db/entity_type.py
+++ b/backend/onyx/db/entity_type.py
@@ -11,7 +11,7 @@
 from onyx.server.kg.models import EntityType
 
 
-_UNGROUNDED_SOURCE_NAME = "Ungrounded"
+UNGROUNDED_SOURCE_NAME = "Ungrounded"
 
 
 def get_entity_types_with_grounded_source_name(
@@ -87,7 +87,7 @@ def get_configured_entity_types(db_session: Session) -> dict[str, list[KGEntityT
 
     et_map = defaultdict(list)
     for et in ets:
-        key = et.grounded_source_name or _UNGROUNDED_SOURCE_NAME
+        key = et.grounded_source_name or UNGROUNDED_SOURCE_NAME
         et_map[key].append(et)
 
     return et_map
diff --git a/backend/onyx/server/kg/api.py b/backend/onyx/server/kg/api.py
index 5608199742..8d15e2c24d 100644
--- a/backend/onyx/server/kg/api.py
+++ b/backend/onyx/server/kg/api.py
@@ -179,15 +179,19 @@ def get_kg_entity_types(
 ) -> SourceAndEntityTypeView:
     # when using for the first time, populate with default entity types
     entity_types = {
-        key: [EntityType.from_model(et) for et in ets]
-        for key, ets in get_configured_entity_types(db_session=db_session).items()
+        source_name: [EntityType.from_model(et) for et in ets]
+        for source_name, ets in get_configured_entity_types(
+            db_session=db_session
+        ).items()
     }
 
     source_statistics = {
-        key: SourceStatistics(
-            source_name=key, last_updated=last_updated, entities_count=entities_count
+        source_name: SourceStatistics(
+            source_name=source_name,
+            last_updated=last_updated,
+            entities_count=entities_count,
         )
-        for key, (
+        for source_name, (
             last_updated,
             entities_count,
         ) in get_entity_stats_by_grounded_source_name(db_session=db_session).items()