diff --git a/setup.py b/setup.py
index d7765b2e..29e282aa 100644
--- a/setup.py
+++ b/setup.py
@@ -60,7 +60,7 @@ def filter_requirements(line):
     install_requires=[
         'MarkupSafe>=1.0',
         'Flask>=1.0.2',
-        'jsonrpcserver>=4.0.1',
+        'jsonrpcserver>=4.0.1,<5',
         'gunicorn>=19.9.0',
         'docutils>=0.14',
         'editdistance>=0.5.3',
diff --git a/src/benchmarkstt/metrics/core.py b/src/benchmarkstt/metrics/core.py
index 9f564b31..cba33860 100644
--- a/src/benchmarkstt/metrics/core.py
+++ b/src/benchmarkstt/metrics/core.py
@@ -328,7 +328,7 @@ def __generate_list_entity(self, list_parsed):
             index_entities.extend(index_entity)
 
         # sort on the position of the first part of the entity
-        index_entities.sort(key=lambda l: l[0])
+        index_entities.sort(key=lambda elem: elem[0])
 
         # copy-past the entity found in the list
         for k_list in index_entities: