diff --git a/src/objective_types.jl b/src/objective_types.jl
index 94a317e86..6abe630c9 100644
--- a/src/objective_types.jl
+++ b/src/objective_types.jl
@@ -1,4 +1,4 @@
-abstract AbstractObjective
+@compat abstract type AbstractObjective end
 type NonDifferentiable{T} <: AbstractObjective
     f
     f_x::T