diff --git a/test/C_API.jl b/test/C_API.jl
index b633910..56eb5e1 100644
--- a/test/C_API.jl
+++ b/test/C_API.jl
@@ -561,7 +561,7 @@ end
 
 function test_copy_failure()
     opt = Opt(:LD_MMA, 2)
-    opt.opt = C_NULL
+    setfield!(opt, :opt, C_NULL)
     @test_throws ErrorException("Error in nlopt_copy") copy(opt)
     return
 end