diff --git a/Project.toml b/Project.toml
index d3d86d1..4c73f79 100644
--- a/Project.toml
+++ b/Project.toml
@@ -4,6 +4,7 @@ authors = ["Takafumi Arakaki <aka.tkf@gmail.com>"]
 version = "0.1.0"
 
 [deps]
+Setfield = "efcf1570-3423-57d1-acb7-fd33fddbac46"
 Transducers = "28d57a85-8fef-5791-bfe6-a80928e7c999"
 
 [compat]
diff --git a/docs/Manifest.toml b/docs/Manifest.toml
index 9b7fd16..12d0d1b 100644
--- a/docs/Manifest.toml
+++ b/docs/Manifest.toml
@@ -161,7 +161,7 @@ uuid = "cf7118a7-6976-5b1a-9a39-7adc72f591a4"
 uuid = "4ec0a83e-493e-50e2-b9ac-8f72acf5a8f5"
 
 [[UnionArrays]]
-deps = ["Transducers"]
+deps = ["Setfield", "Transducers"]
 path = ".."
 uuid = "d6dd79e4-993b-11e9-1366-0de1c9fe1122"
 version = "0.1.0"
diff --git a/src/impl/arrays.jl b/src/impl/arrays.jl
index d719ee4..4ccbd0d 100644
--- a/src/impl/arrays.jl
+++ b/src/impl/arrays.jl
@@ -3,15 +3,23 @@ struct UnionArray{T, N, P} <: Abstract.UnionArray{T, N}
 
     function UnionArray(parent::P) where {T, N, P <: AbstractArray{T, N}}
         # Make sure that `A.parent` is not a UnionArray/Vector
-        P <: UnionArrayImpls && throw(MethodError(UnionArray, (A,)))
+        P <: UnionArrayImpls && throw(MethodError(UnionArray, (parent,)))
         return new{T, N, P}(parent)
     end
 end
 
 const UnionArrayImpls = Union{UnionVector, UnionArray}
 
-default_reshape(A::UnionVector, dims::T) where T =
-    invoke(reshape, Tuple{AbstractArray, T}, A, dims)
+# A very minimal dummy array implementation just for implementing `default_reshape`:
+struct DummyArray{N} <: AbstractArray{Any,N}
+    dims::NTuple{N,Int}
+end
+Base.size(A::DummyArray) = A.dims
+
+function default_reshape(A::UnionVector, dims::T) where {T}
+    dummy = reshape(DummyArray(size(A)), dims)
+    return @set dummy.parent = A
+end
 
 ua_reshape(A::UnionVector, dims) = UnionArray(default_reshape(A, dims))
 ua_reshape(A::UnionArray, dims) = UnionArray(reshape(A.parent, dims))
diff --git a/src/impl/impl.jl b/src/impl/impl.jl
index 26c3825..77b90a6 100644
--- a/src/impl/impl.jl
+++ b/src/impl/impl.jl
@@ -3,6 +3,7 @@ module Impl
 using Base: Dims
 using Transducers
 using Transducers: @return_if_reduced, next, complete
+using Setfield: @set  # using Setfield instead of Accessors for older Julia
 
 using ..Abstract
 
diff --git a/test/environments/main/Manifest.toml b/test/environments/main/Manifest.toml
index 9233f62..912282d 100644
--- a/test/environments/main/Manifest.toml
+++ b/test/environments/main/Manifest.toml
@@ -195,7 +195,7 @@ uuid = "cf7118a7-6976-5b1a-9a39-7adc72f591a4"
 uuid = "4ec0a83e-493e-50e2-b9ac-8f72acf5a8f5"
 
 [[UnionArrays]]
-deps = ["Transducers"]
+deps = ["Setfield", "Transducers"]
 path = "../../.."
 uuid = "d6dd79e4-993b-11e9-1366-0de1c9fe1122"
 version = "0.1.0"