diff --git a/activitysim/core/estimation.py b/activitysim/core/estimation.py
index d320cc931..4d4836708 100644
--- a/activitysim/core/estimation.py
+++ b/activitysim/core/estimation.py
@@ -328,7 +328,7 @@ def write_parquet(self, df, file_path, index, append=False):
         ), f"file already exists: {file_path}"
 
         # Explicitly set the data types of the columns
-        for col_name, col_data in df.iteritems():
+        for col_name, col_data in df.items():
             if "int" in str(col_data.dtype):
                 pass
             elif (