diff --git a/cadc-access-control/src/main/java/ca/nrc/cadc/ac/client/GroupAuthorizer.java b/cadc-access-control/src/main/java/ca/nrc/cadc/ac/client/GroupAuthorizer.java
index fb2361a94e507e573c121c81f898f7ae9ea34648..11b8ac2a3495b8c5cd771e87cdd21ab86907b089 100644
--- a/cadc-access-control/src/main/java/ca/nrc/cadc/ac/client/GroupAuthorizer.java
+++ b/cadc-access-control/src/main/java/ca/nrc/cadc/ac/client/GroupAuthorizer.java
@@ -87,6 +87,14 @@ public class GroupAuthorizer implements Authorizer
 
     private GroupURI groupURI;
     
+    private GroupAuthorizer() { }
+    
+    /**
+     * Create an authorizer that allows members of the specified group and denies
+     * all other users. The string argument must be a valid GroupURI.
+     * 
+     * @param uri group identifier for the allow group
+     */
     public GroupAuthorizer(String uri) 
     { 
         try