diff --git a/toardb/timeseries/crud.py b/toardb/timeseries/crud.py
index 03480e8768b95ddef0113fe797eb002d218c2608..a38ba93ea9264d0b3a32b144fed2a302f308e649 100644
--- a/toardb/timeseries/crud.py
+++ b/toardb/timeseries/crud.py
@@ -20,7 +20,7 @@ def get_timeseries(db: Session, timeseries_id: int):
     db_object = db.query(models.Timeseries).filter(models.Timeseries.id == timeseries_id).first()
     # there is a mismatch with additional_metadata
     if db_object:
-        db_object.additional_metadata = str(db_object.additional_metadata)
+        db_object.additional_metadata = str(db_object.additional_metadata).replace("'",'"')
     return db_object
 
 
@@ -28,7 +28,7 @@ def get_all_timeseries(db: Session, skip : int = 0, limit: int = None):
     db_objects = db.query(models.Timeseries).offset(skip).limit(limit).all()
     for db_object in db_objects:
         # there is a mismatch with additional_metadata
-        db_object.additional_metadata = str(db_object.additional_metadata)
+        db_object.additional_metadata = str(db_object.additional_metadata).replace("'",'"')
     return db_objects
 
 
@@ -39,7 +39,7 @@ def get_timeseries_by_unique_constraints(db: Session, station_id: int, variable_
                                       .first()
     # there is a mismatch with additional_metadata
     if db_object:
-        db_object.additional_metadata = str(db_object.additional_metadata)
+        db_object.additional_metadata = str(db_object.additional_metadata).replace("'",'"')
     return db_object
 
 
@@ -125,5 +125,5 @@ def create_timeseries(db: Session, timeseries: TimeseriesCreate):
     # there is a mismatch with additional_metadata
     # in upload command, we have now: "additional_metadata": "{}"
     # but return from this method gives (=database): "additional_metadata": {}
-    db_timeseries.additional_metadata = str(db_timeseries.additional_metadata)
+    db_timeseries.additional_metadata = str(db_timeseries.additional_metadata).replace("'",'"')
     return db_timeseries