diff --git a/string_grouper/string_grouper.py b/string_grouper/string_grouper.py
index 0d8a5ac6..69b7a87c 100644
--- a/string_grouper/string_grouper.py
+++ b/string_grouper/string_grouper.py
@@ -1147,7 +1147,7 @@ def _validate_strings_exist(master_side, dupe_side, master_strings, dupe_strings
     def _is_series_of_strings(series_to_test: pd.Series) -> bool:
         if not isinstance(series_to_test, pd.Series):
             return False
-        elif series_to_test.to_frame().applymap(
+        elif series_to_test.to_frame().map(
                     lambda x: not isinstance(x, str)
                 ).squeeze(axis=1).any():
             return False