diff --git a/src/container.jl b/src/container.jl
index a1d0b83..4186a06 100644
--- a/src/container.jl
+++ b/src/container.jl
@@ -1,13 +1,18 @@
 
 """
-    UndefProperty
+    UndefProperty{T}
 
 Placeholder for undefined properties in [`Container`](@ref).
 """
-struct UndefProperty end
+struct UndefProperty{T} end
+
+UndefProperty() = UndefProperty{Any}()
 
 Base.show(io::IO, ::UndefProperty) = print(io, "#undef")
 
+undeftypeof(::UndefProperty{T}) where {T} = T
+undeftypeof(obj) = typeof(obj)
+
 """
     Container{T}
 
@@ -22,8 +27,8 @@ Create an uninitialized container for `T`.
 ```jldoctest
 julia> Container{Complex{Int64}}()
 Container{Complex{Int64}}:
-  re: #undef
-  im: #undef
+  re: Int64 = #undef
+  im: Int64 = #undef
 ```
 """
 struct Container{T}
@@ -39,7 +44,7 @@ end
 
 Base.getproperty(obj::Container{T}, name::Symbol) where {T} = get(getfield(obj, 1), name) do
     if name in fieldnames(T)
-        UndefProperty()
+        UndefProperty{fieldtype(T, name)}()
     else
         error("type $T has no field $name")
     end
@@ -73,13 +78,9 @@ function Base.show(io::IO, mime::MIME"text/plain", obj::Container)
         print(io, "  ")
         print(io, prop)
         print(io, ": ")
-        if val isa UndefProperty
-            show(io, val)
-        else
-            show(io, typeof(val))
-            print(io, " = ")
-            show(io, mime, val)
-        end
+        show(io, undeftypeof(val))
+        print(io, " = ")
+        show(io, mime, val)
         print(io, "\n")
     end
 end
diff --git a/src/macro.jl b/src/macro.jl
index 0a08840..3173106 100644
--- a/src/macro.jl
+++ b/src/macro.jl
@@ -158,9 +158,6 @@ end
 function deducefieldtypes!(fields::Vector{>:FieldInfo})
     namedfields = filter(field -> field.name isa Symbol, fields)
     for field in fields
-        if field.type != UndefProperty
-            continue
-        end
         thistype = NamedTuple{tuple(map(field -> field.name, namedfields)...), Tuple{map(field -> field.type, namedfields)...}}
         fieldconstype = deducetype(field.tfunc, thistype)
         if fieldconstype !== Union{}
@@ -232,7 +229,7 @@ function generateserializemethod(constructname::Symbol, structname::Symbol, fiel
             push!(sercalls, field.line)
         end
         if isnothing(field.name)
-            fielddata = UndefProperty()
+            fielddata = UndefProperty{field.type}()
         else
             fielddata = Expr(:(.),
                 this,
@@ -370,7 +367,7 @@ function generateestimatesizemethod(constructname::Symbol, structname::Symbol, f
             ),
             escape_excludes(field.cons, [this])
         )
-        # if the construct can't accept UndefProperty() while the code has it,
+        # if the construct can't accept UndefProperty{T}() while the code has it,
         # the size is just UnboundedSize(0) (like any other unknown sized construct)
         szcall = Expr(:try,
             Expr(:block, szcall),
diff --git a/test/runtests.jl b/test/runtests.jl
index 2598a09..033bac9 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -84,7 +84,7 @@ end
         @test repr(UndefProperty()) == "#undef"
         @test_throws ArgumentError Container(1)
         @test Container(im).im
-        @test Container{Complex{Bool}}().im == UndefProperty()
+        @test Container{Complex{Bool}}().im == UndefProperty{Bool}()
         @test_throws ErrorException Container{Complex{Bool}}().i
         @test_throws ErrorException Container(im).im = false
         @test propertynames(Container(1//2)) == propertynames(1//2)
@@ -98,8 +98,8 @@ end
         """
         @test repr("text/plain", Container{Complex{Int64}}()) == """
         Container{Complex{Int64}}:
-          re: #undef
-          im: #undef
+          re: Int64 = #undef
+          im: Int64 = #undef
         """
     end
     @testset "primitive io" begin
@@ -377,6 +377,11 @@ end
         @test_throws ValidationError serialize(Const(0x0102), 0x0201)
     end
     @testset "Overwrite" begin
+        @testset "deduce type" begin
+            @test Constructs.deducetype((v) -> Overwrite(UInt8, v), UInt8) <: Construct{UInt8}
+            @test Constructs.deducetype((v) -> Overwrite(UInt8, v), Function) <: Construct{UInt8}
+            @test Constructs.deducetype((v) -> Overwrite(UInt8, v), UndefProperty) <: Construct{UInt8}
+        end
         @test_throws ArgumentError Overwrite(UInt8, () -> 0x01)
         @test serialize(Overwrite(UInt8, 0x01), 2) == b"\x01"
         @test serialize(Overwrite(UInt8, 0x02), UndefProperty()) == b"\x02"