diff --git a/src/GEOparse/GEOTypes.py b/src/GEOparse/GEOTypes.py
index 3e9f377..fe65017 100755
--- a/src/GEOparse/GEOTypes.py
+++ b/src/GEOparse/GEOTypes.py
@@ -432,7 +432,7 @@ def annotate_and_average(
         if merge_on_column:
             logger.info("merge_on_column is not None. Using this option.")
             tmp_data = self.table.merge(gpl.table, on=merge_on_column, how="outer")
-            tmp_data = tmp_data.groupby(group_by_column).mean()[[expression_column]]
+            tmp_data = tmp_data.groupby(group_by_column)[[expression_column]].mean()
         else:
             if gpl_on is None or gsm_on is None:
                 raise Exception(
@@ -442,7 +442,7 @@ def annotate_and_average(
             tmp_data = self.table.merge(
                 gpl.table, left_on=gsm_on, right_on=gpl_on, how="outer"
             )
-            tmp_data = tmp_data.groupby(group_by_column).mean()[[expression_column]]
+            tmp_data = tmp_data.groupby(group_by_column)[[expression_column]].mean()
         if rename:
             tmp_data.columns = [self.name]
         return tmp_data
diff --git a/tox.ini b/tox.ini
index 253e679..55a0602 100644
--- a/tox.ini
+++ b/tox.ini
@@ -6,7 +6,8 @@ envlist = py38,
 changedir = tests
 basepython =
     py38: python3.8
-passenv = GEOPARSE_USE_HTTP_FOR_FTP *_proxy *_PROXY USER
+passenv = GEOPARSE_USE_HTTP_FOR_FTP,*_proxy,*_PROXY,USER
 commands = pytest {posargs}
 deps = -r{toxinidir}/requirements.txt
+       lxml
 commands-pre = pip install ..