diff --git a/pam.py b/pam.py
index 0042456..237f13d 100644
--- a/pam.py
+++ b/pam.py
@@ -175,6 +175,13 @@ def my_conv(n_messages, messages, p_response, app_data):
         return auth_success
 
 
+def authenticate(*vargs, **dargs):
+    """
+    Compatibility function for older versions of python-pam.
+    """
+    return pam().authenticate(*vargs, **dargs)
+
+
 if __name__ == "__main__":
     import readline, getpass