diff --git a/src/pricehist/sources/coinmarketcap.py b/src/pricehist/sources/coinmarketcap.py
index 0d04b62..2d6692b 100644
--- a/src/pricehist/sources/coinmarketcap.py
+++ b/src/pricehist/sources/coinmarketcap.py
@@ -1,6 +1,6 @@
 import dataclasses
 import json
-from datetime import datetime
+from datetime import datetime, timezone
 from decimal import Decimal
 
 import requests
@@ -77,10 +77,19 @@ class CoinMarketCap(BaseSource):
             params["convert"] = series.quote
 
         params["time_start"] = int(
-            int(datetime.strptime(series.start, "%Y-%m-%d").timestamp())
+            int(
+                datetime.strptime(series.start, "%Y-%m-%d")
+                .replace(tzinfo=timezone.utc)
+                .timestamp()
+            )
         )
         params["time_end"] = (
-            int(datetime.strptime(series.end, "%Y-%m-%d").timestamp()) + 24 * 60 * 60
+            int(
+                datetime.strptime(series.end, "%Y-%m-%d")
+                .replace(tzinfo=timezone.utc)
+                .timestamp()
+            )
+            + 24 * 60 * 60
         )  # round up to include the last day
 
         response = self.log_curl(requests.get(url, params=params))
diff --git a/src/pricehist/sources/yahoo.py b/src/pricehist/sources/yahoo.py
index c0b4d15..0a61cb5 100644
--- a/src/pricehist/sources/yahoo.py
+++ b/src/pricehist/sources/yahoo.py
@@ -2,7 +2,7 @@ import csv
 import dataclasses
 import json
 import logging
-from datetime import datetime
+from datetime import datetime, timezone
 from decimal import Decimal
 
 import requests
@@ -102,8 +102,16 @@ class Yahoo(BaseSource):
         )
         spark = json.loads(spark_response.content)
 
-        start_ts = int(datetime.strptime(series.start, "%Y-%m-%d").timestamp())
-        end_ts = int(datetime.strptime(series.end, "%Y-%m-%d").timestamp()) + (
+        start_ts = int(
+            datetime.strptime(series.start, "%Y-%m-%d")
+            .replace(tzinfo=timezone.utc)
+            .timestamp()
+        )
+        end_ts = int(
+            datetime.strptime(series.end, "%Y-%m-%d")
+            .replace(tzinfo=timezone.utc)
+            .timestamp()
+        ) + (
             24 * 60 * 60
         )  # round up to include the last day