diff --git a/src/main.py b/src/main.py
index 187073c..13b143b 100644
--- a/src/main.py
+++ b/src/main.py
@@ -202,9 +202,6 @@ def get_slot_by_id(
     if not event:
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Slot not found")
 
-    if event.summary != TITLE_FREE:
-        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Slot is busy")
-
     return event
 
 
@@ -216,6 +213,9 @@ def mark_busy_calendar_slot_by_id(
 ):
     event = get_slot_by_id(slot_id=slot_id)
 
+    if event.summary != TITLE_FREE:
+        raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="Slot is busy")
+
     event.summary = TITLE_BUSY
     event.colorId = COLOR_BUSY
     if description: