diff --git a/backend/routers/sleep.py b/backend/routers/sleep.py
index 2c84480..87753ec 100644
--- a/backend/routers/sleep.py
+++ b/backend/routers/sleep.py
@@ -164,6 +164,10 @@ def create_sleep(
     """Create or update sleep entry (upsert by date)."""
     pid = session['profile_id']
 
+    # Convert empty strings to None for TIME fields
+    bedtime = data.bedtime if data.bedtime else None
+    wake_time = data.wake_time if data.wake_time else None
+
     with get_db() as conn:
         cur = get_cursor(conn)
 
@@ -191,7 +195,7 @@ def create_sleep(
                 updated_at = CURRENT_TIMESTAMP
             RETURNING *
         """, (
-            pid, data.date, data.bedtime, data.wake_time, data.duration_minutes,
+            pid, data.date, bedtime, wake_time, data.duration_minutes,
             data.quality, data.wake_count, data.deep_minutes, data.rem_minutes,
             data.light_minutes, data.awake_minutes, data.note, data.source
         ))
@@ -210,6 +214,10 @@ def update_sleep(
     """Update existing sleep entry by ID."""
     pid = session['profile_id']
 
+    # Convert empty strings to None for TIME fields
+    bedtime = data.bedtime if data.bedtime else None
+    wake_time = data.wake_time if data.wake_time else None
+
     with get_db() as conn:
         cur = get_cursor(conn)
 
@@ -230,7 +238,7 @@ def update_sleep(
             WHERE id = %s AND profile_id = %s
             RETURNING *
         """, (
-            data.date, data.bedtime, data.wake_time, data.duration_minutes,
+            data.date, bedtime, wake_time, data.duration_minutes,
             data.quality, data.wake_count, data.deep_minutes, data.rem_minutes,
             data.light_minutes, data.awake_minutes, data.note, id, pid
         ))