diff --git a/awscli/botocore/httpsession.py b/awscli/botocore/httpsession.py
index ae657c6..0155958 100644
--- a/awscli/botocore/httpsession.py
+++ b/awscli/botocore/httpsession.py
@@ -87,7 +87,9 @@ if hasattr(PoolKey, 'key_blocksize'):
 
 try:
     from certifi import where
+    DEFAULT_CA_BUNDLE = where()
 except ImportError:
+    raise
 
     def where():
         return DEFAULT_CA_BUNDLE