diff --git a/src/Compat.jl b/src/Compat.jl
index e240e6348..c26feb572 100644
--- a/src/Compat.jl
+++ b/src/Compat.jl
@@ -1450,6 +1450,11 @@ if VERSION < v"0.6.0-dev.838"
     Base.convert{T}(::Type{Set{T}}, s::Set) = Set{T}(s)
 end
 
+# https://github.com/JuliaLang/julia/pull/18082
+if VERSION < v"0.6.0-dev.2347"
+    Base.isassigned(x::Base.RefValue) = isdefined(x, :x)
+end
+
 include("to-be-deprecated.jl")
 
 end # module Compat
diff --git a/test/runtests.jl b/test/runtests.jl
index 41bc349c3..3280a1f04 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1805,6 +1805,10 @@ let
     @test cssset == Set(["foo", "bar"])
 end
 
+# PR 18082
+@test !isassigned(Ref{String}())
+@test isassigned(Ref{String}("Test"))
+
 include("to-be-deprecated.jl")
 
 nothing