diff --git a/dataframely/columns/string.py b/dataframely/columns/string.py
index fadb4f2..f558485 100644
--- a/dataframely/columns/string.py
+++ b/dataframely/columns/string.py
@@ -78,9 +78,9 @@ def dtype(self) -> pl.DataType:
     def validation_rules(self, expr: pl.Expr) -> dict[str, pl.Expr]:
         result = super().validation_rules(expr)
         if self.min_length is not None:
-            result["min_length"] = expr.str.len_bytes() >= self.min_length
+            result["min_length"] = expr.str.len_chars() >= self.min_length
         if self.max_length is not None:
-            result["max_length"] = expr.str.len_bytes() <= self.max_length
+            result["max_length"] = expr.str.len_chars() <= self.max_length
         if self.regex is not None:
             result["regex"] = expr.str.contains(self.regex)
         return result