diff --git a/forest/oak/base.py b/forest/oak/base.py
index e45b0cdd..03dc4a4a 100644
--- a/forest/oak/base.py
+++ b/forest/oak/base.py
@@ -473,10 +473,10 @@ def run(study_folder: str, output_folder: str, tz_str: Optional[str] = None,
         file_list.sort()
 
         # transform all files in folder to datelike format
-        if "+00_00.csv" in file_list[0]:
-            file_dates = [file.replace("+00_00.csv", "") for file in file_list]
-        else:
-            file_dates = [file.replace(".csv", "") for file in file_list]
+        file_dates = [
+            file.replace(".csv", "").replace("+00_00", "")
+            for file in file_list
+        ]
 
         # process dates
         dates = [datetime.strptime(file, fmt) for file in file_dates]