diff --git a/sourcing/view.py b/sourcing/view.py
index 350a099..a9f2f6e 100644
--- a/sourcing/view.py
+++ b/sourcing/view.py
@@ -320,8 +320,11 @@ def build_links():
         save_new_xanalink(doc1, doc2)
         return redirect(url_for(request.endpoint, doc1=hashid1, doc2=hashid2))
 
-    links = list({i for i in doc1.subjects} &
-                 {i for i in doc2.subjects})
+    if doc1 and doc2:
+        links = list({i for i in doc1.subjects} &
+                     {i for i in doc2.subjects})
+    else:
+        links = []
 
     return render_template('build_links.html',
                            iter_lines=iter_lines,