diff --git a/src/parameters_base.jl b/src/parameters_base.jl
index 61c17d4..dfbc54d 100644
--- a/src/parameters_base.jl
+++ b/src/parameters_base.jl
@@ -18,3 +18,4 @@ value(x::AbstractArray) = map(value, x)
 value(x::Tuple) = map(value, x)
 value(x::NamedTuple) = map(value, x)
 value(x::Dict) = Dict(k => value(v) for (k, v) in x)
+value(::Nothing) = nothing
diff --git a/test/parameters.jl b/test/parameters.jl
index 6f8e17a..7df5d2d 100644
--- a/test/parameters.jl
+++ b/test/parameters.jl
@@ -62,7 +62,7 @@
     end
 
     @testset "value_flatten" begin
-        x = (ones(3), fixed(5.0), (a=fixed(5.0), b=[6.0, 2.1]))
+        x = (ones(3), fixed(5.0), (a=fixed(5.0), b=[6.0, 2.1]), nothing)
         v, unflatten = value_flatten(x)
 
         @test length(v) == 5