diff --git a/dbt/adapters/vertica/impl.py b/dbt/adapters/vertica/impl.py
index 9c2c987..53b5583 100644
--- a/dbt/adapters/vertica/impl.py
+++ b/dbt/adapters/vertica/impl.py
@@ -13,7 +13,7 @@ def date_function(cls):
     @classmethod
     def convert_text_type(cls, agate_table, col_idx):
         column = agate_table.columns[col_idx]
-        lens = (len(d.encode("utf-8")) for d in column.values_without_nulls())
+        lens = [len(d.encode("utf-8")) for d in column.values_without_nulls()]
         max_len = max(lens) if lens else 64
         return "varchar({})".format(max_len)