diff --git a/networks.rkt b/networks.rkt
index 3328a74..931bef3 100644
--- a/networks.rkt
+++ b/networks.rkt
@@ -473,11 +473,11 @@
          [(and (member '> impacts) (not (member '< impacts))) '>]
          [(equal? impacts '(=)) '=]
          [else 0]))))
-  (match interactions
-    [(list '<) 1]
-    [(list '>) -1]
-    [(list '=) #f]
-    [_ 0]))
+  (cond
+    [(and (member '< interactions) (not (member '> interactions))) 1]
+    [(and (member '> interactions) (not (member '< interactions))) -1]
+    [(equal? interactions '(=)) #f]
+    [else 0]))
 
 (module+ test
   (test-case "get-interaction-sign"
@@ -491,6 +491,7 @@
     (check-equal? (get-interaction-sign n-bool bool-doms 'x 'y) 1)
     (check-equal? (get-interaction-sign n-bool bool-doms 'y 'x) -1)
     (check-false (get-interaction-sign n-bool bool-doms 'x 'z))
+    (check-equal? (get-interaction-sign n-bool bool-doms 'y 'z) 1)
     (check-equal? (get-interaction-sign n-bool bool-doms 'x 't) 0)
     (define n-multi (network-form->network
                      (hash 'x '(min (+ y 1) 2)