diff --git a/networks.rkt b/networks.rkt
index 931bef3..a8bad84 100644
--- a/networks.rkt
+++ b/networks.rkt
@@ -502,7 +502,8 @@
     (check-false (get-interaction-sign n-multi 123-doms 'x 'y))
     (check-equal? (get-interaction-sign n-multi 123-doms 'y 'x) 1)
     (check-equal? (get-interaction-sign n-multi 123-doms 'y 'z) -1)
-    (check-equal? (get-interaction-sign n-multi 123-doms 'y 't) 0)))
+    (check-equal? (get-interaction-sign n-multi 123-doms 'y 't) 0)
+    (check-equal? (get-interaction-sign n-multi 123-doms 'y 'y) 1)))
 
 ;;; Given a network, builds its interaction graph.  The graph has
 ;;; variables as nodes and has a directed edge from x to y if