diff --git a/osaca/semantics/hw_model.py b/osaca/semantics/hw_model.py
index ef6a61d..a904b32 100755
--- a/osaca/semantics/hw_model.py
+++ b/osaca/semantics/hw_model.py
@@ -318,7 +318,8 @@ class MachineModel(object):
             # Check if modification date of DB is older than cached version
             if os.path.getmtime(filepath) < os.path.getmtime(cachepath):
                 # load cached version
-                cached_db = pickle.load(open(cachepath, 'rb'))
+                with open(cachepath, 'rb') as f:
+                    cached_db = pickle.load(f)
                 return cached_db
             else:
                 # DB newer than cached version --> delete cached file and return False
diff --git a/setup.py b/setup.py
index 8604f3d..2e380b8 100755
--- a/setup.py
+++ b/setup.py
@@ -91,8 +91,8 @@ setup(
     # https://packaging.python.org/en/latest/requirements.html
     install_requires=[
         'networkx',
-        'pyparsing',
-        'ruamel.yaml',
+        'pyparsing>=2.3.1',
+        'ruamel.yaml>=0.15.71',
     ],
     python_requires='>=3.5',