diff --git a/tests/src/test/scala/cats/tests/RepresentableSuite.scala b/tests/src/test/scala/cats/tests/RepresentableSuite.scala
index 2455d5fd4e..413a1a86c3 100644
--- a/tests/src/test/scala/cats/tests/RepresentableSuite.scala
+++ b/tests/src/test/scala/cats/tests/RepresentableSuite.scala
@@ -59,6 +59,7 @@ class RepresentableSuite extends CatsSuite {
   }
 
   {
+    implicit val isoFunction1 = Isomorphisms.invariant[String => ?]
     implicit val monadInstance = Representable.monad[String => ?]
     checkAll("String => ?", MonadTests[String => ?].monad[String, String, String])
   }