diff --git a/src/ColumnImplementations.jl b/src/ColumnImplementations.jl
index b810a3e..31f06bc 100644
--- a/src/ColumnImplementations.jl
+++ b/src/ColumnImplementations.jl
@@ -18,6 +18,7 @@ our Attr Variable indices with the Julia type of Int
 end 
 Base.isless(x::AttrVar,y::AttrVar) = x.val < y.val
 Base.convert(::Type{T}, x::T) where {T>:Union{Nothing,AttrVar}} = x
+Base.convert(::Type{T}, x::T) where {T>:Union{Missing,AttrVar}} = x
 Base.convert(::Type{T}, x::T) where {T>:AttrVar} = x
 Base.convert(::Type{T}, x) where {T>:AttrVar} = convert(Base.typesplit(T, AttrVar), x)
 
diff --git a/src/PreimageCaches.jl b/src/PreimageCaches.jl
index 6034436..205fe8a 100644
--- a/src/PreimageCaches.jl
+++ b/src/PreimageCaches.jl
@@ -107,6 +107,14 @@ function preimage(dom, m::Mapping{S,T}, ::TrivialCache{S,T}, y) where {S,T}
   [x for x in dom if get(m, x, nothing) == y]
 end
 
+function preimage(dom, m::Mapping{S,T}, ::TrivialCache{S,T}, y::Missing) where {S,T>:Union{Missing}}
+  [x for x in dom if ismissing(get(m, x, nothing))]
+end
+
+function preimage(dom, m::Mapping{S,T}, ::TrivialCache{S,T}, y) where {S,T>:Union{Missing}}
+  [x for x in dom if coalesce(get(m, x, nothing) == y, false)]
+end
+
 function preimage_multi(dom, m::Mapping{S,T}, pc::TrivialCache{S,T}, ys) where {S,T}
   map(y -> preimage(dom, m, pc, y), ys)
 end
diff --git a/test/Columns.jl b/test/Columns.jl
index 7087a19..c29bc51 100644
--- a/test/Columns.jl
+++ b/test/Columns.jl
@@ -42,4 +42,32 @@ for coltype in coltypes
   @test collect(preimage(OneTo(3), col, :A)) == [1]
 end
 
+# Int → Union type columns
+#---------------------
+
+coltypes = [
+  column_type(AttrChoice(Union{Symbol,Nothing}), NoIndex, sparsity)
+  for sparsity in [Dense, Sparse(Int)]
+]
+
+for coltype in coltypes
+  col = coltype(1=>:A,2=>:B,3=>nothing)
+  @test isempty(preimage(OneTo(3), col, :F))
+  @test collect(preimage(OneTo(3), col, :A)) == [1]
+  @test collect(preimage(OneTo(3), col, nothing)) == [3]
+end
+
+coltypes = [
+  column_type(AttrChoice(Union{Symbol,Missing}), NoIndex, sparsity)
+  for sparsity in [Dense, Sparse(Int)]
+]
+
+for coltype in coltypes
+  col = coltype(1=>:A,2=>:B,3=>missing)
+  @test isempty(preimage(OneTo(3), col, :F))
+  @test collect(preimage(OneTo(3), col, :A)) == [1]
+  @test collect(preimage(OneTo(3), col, missing)) == [3]
+end
+
+
 end # module