diff --git a/my/body/sleep/common.py b/my/body/sleep/common.py
index 7bc1021..e84c8d5 100644
--- a/my/body/sleep/common.py
+++ b/my/body/sleep/common.py
@@ -17,15 +17,21 @@ class Combine:
             bdf = BM.dataframe()
             temp = bdf['temp']
 
+            # sort index and drop nans, otherwise indexing with [start: end] gonna complain
+            temp = pd.Series(
+                temp.values,
+                index=pd.to_datetime(temp.index, utc=True)
+            ).sort_index()
+            temp = temp.loc[temp.index.dropna()]
+
             def calc_avg_temperature(row):
                 start = row['sleep_start']
                 end   = row['sleep_end']
                 if pd.isna(start) or pd.isna(end):
                     return None
 
-                between = (start <= temp.index) & (temp.index <= end)
                 # on no temp data, returns nan, ok
-                return temp[between].mean()
+                return temp[start: end].mean()
 
             df['avg_temp'] = df.apply(calc_avg_temperature, axis=1)
         return df