diff --git a/Project.toml b/Project.toml
index a1322d7..c1cec25 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "ParameterHandling"
 uuid = "2412ca09-6db7-441c-8e3a-88d5709968c5"
 authors = ["Invenia Technical Computing Corporation"]
-version = "0.4.0"
+version = "0.4.1"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
diff --git a/src/flatten.jl b/src/flatten.jl
index 717b27b..3859a7a 100644
--- a/src/flatten.jl
+++ b/src/flatten.jl
@@ -31,7 +31,10 @@ function flatten(::Type{T}, x::R) where {T<:Real,R<:Real}
     return v, unflatten_to_Real
 end
 
-flatten(::Type{T}, x::Vector{R}) where {T<:Real,R<:Real} = (Vector{T}(x), Vector{R})
+function flatten(::Type{T}, x::Vector{R}) where {T<:Real,R<:Real}
+    unflatten_to_Vector(v) = Vector{R}(v)
+    return Vector{T}(x), unflatten_to_Vector
+end
 
 function _flatten_vector_integer(::Type{T}, x::AbstractVector{<:Integer}) where {T<:Real}
     unflatten_to_Vector_Integer(x_vec) = x
diff --git a/src/parameters.jl b/src/parameters.jl
index a0e18b9..cf782a2 100644
--- a/src/parameters.jl
+++ b/src/parameters.jl
@@ -150,7 +150,7 @@ value(x::Deferred) = x.f(value(x.args)...)
 
 function flatten(::Type{T}, x::Deferred) where {T<:Real}
     v, unflatten = flatten(T, x.args)
-    unflatten_Deferred(v_new::Vector{T}) = Deferred(x.f, unflatten(v_new))
+    @inline unflatten_Deferred(v_new::Vector{T}) = Deferred(x.f, unflatten(v_new))
     return v, unflatten_Deferred
 end
 
diff --git a/src/test_utils.jl b/src/test_utils.jl
index 22ce3d3..2a1e5fa 100644
--- a/src/test_utils.jl
+++ b/src/test_utils.jl
@@ -43,6 +43,7 @@ function test_flatten_interface(x::T; check_inferred::Bool=true) where {T}
 
         # Check that everything infers properly.
         check_inferred && @inferred flatten(x)
+        check_inferred && @inferred unflatten(v)
 
         # Test with different precisions
         @testset "Float64" begin
@@ -54,6 +55,7 @@ function test_flatten_interface(x::T; check_inferred::Bool=true) where {T}
 
             # Check that everything infers properly.
             check_inferred && @inferred flatten(Float64, x)
+            check_inferred && @inferred _unflatten(_v)
         end
         @testset "Float32" begin
             _v, _unflatten = flatten(Float32, x)
@@ -63,6 +65,7 @@ function test_flatten_interface(x::T; check_inferred::Bool=true) where {T}
 
             # Check that everything infers properly.
             check_inferred && @inferred flatten(Float32, x)
+            check_inferred && @inferred _unflatten(_v)
         end
         @testset "Float16" begin
             _v, _unflatten = flatten(Float16, x)
@@ -72,6 +75,7 @@ function test_flatten_interface(x::T; check_inferred::Bool=true) where {T}
 
             # Check that everything infers properly.
             check_inferred && @inferred flatten(Float16, x)
+            check_inferred && @inferred _unflatten(_v)
         end
     end