diff --git a/test/interval_tests/forwarddiff.jl b/test/interval_tests/forwarddiff.jl
index 7d48f3d0b..57230ad0a 100644
--- a/test/interval_tests/forwarddiff.jl
+++ b/test/interval_tests/forwarddiff.jl
@@ -62,6 +62,8 @@ end
 
         # g(x) = 2^x # not guaranteed
 
-        @test f′(0) === df(0)
+        @test isequal_interval(f′(0), df(0))
+        @test isguaranteed(f′(0))
+        @test !isguaranteed(df(0))
     end
 end