diff --git a/base/array.jl b/base/array.jl
index 91e9f800f8cb4..76d1883d17af5 100644
--- a/base/array.jl
+++ b/base/array.jl
@@ -664,6 +664,14 @@ end
 _array_for(::Type{T}, itr, ::HasLength) where {T} = Array{T,1}(Int(length(itr)::Integer))
 _array_for(::Type{T}, itr, ::HasShape) where {T} = similar(Array{T}, indices(itr))
 
+function _isconcreteunion(::Type{T}) where T
+    if T isa Union
+        _isconcreteunion(T.a) && _isconcreteunion(T.b)
+    else
+        isconcrete(T)
+    end
+end
+
 function collect(itr::Generator)
     isz = iteratorsize(itr.iter)
     et = _default_eltype(typeof(itr))
@@ -675,7 +683,9 @@ function collect(itr::Generator)
             return _array_for(et, itr.iter, isz)
         end
         v1, st = next(itr, st)
-        collect_to_with_first!(_array_for(typeof(v1), itr.iter, isz), v1, itr, st)
+        S = _default_eltype(typeof(itr))
+        T = _isconcreteunion(S) ? S : typeof(v1)
+        collect_to_with_first!(_array_for(T, itr.iter, isz), v1, itr, st)
     end
 end
 
@@ -688,7 +698,9 @@ function _collect(c, itr, ::EltypeUnknown, isz::Union{HasLength,HasShape})
         return _similar_for(c, _default_eltype(typeof(itr)), itr, isz)
     end
     v1, st = next(itr, st)
-    collect_to_with_first!(_similar_for(c, typeof(v1), itr, isz), v1, itr, st)
+    S = _default_eltype(typeof(itr))
+    T = _isconcreteunion(S) ? S : typeof(v1)
+    collect_to_with_first!(_similar_for(c, T, itr, isz), v1, itr, st)
 end
 
 function collect_to_with_first!(dest::AbstractArray, v1, itr, st)
diff --git a/test/arrayops.jl b/test/arrayops.jl
index 70997260272ea..627afde46758f 100644
--- a/test/arrayops.jl
+++ b/test/arrayops.jl
@@ -1207,6 +1207,10 @@ end
     @test isequal([1,2,3], [a for (a,b) in enumerate(2:4)])
     @test isequal([2,3,4], [b for (a,b) in enumerate(2:4)])
 
+    @test [s for s in Union{String, Void}["a", nothing]] isa Vector{Union{String, Void}}
+    @test [s for s in Union{String, Void}["a"]] isa Vector{Union{String, Void}}
+    @test [s for s in Vector{Union{String, Void}}()] isa Vector{Union{String, Void}}
+
     @testset "comprehension in let-bound function" begin
         let x⊙y = sum([x[i]*y[i] for i=1:length(x)])
             @test [1,2] ⊙ [3,4] == 11
diff --git a/test/functional.jl b/test/functional.jl
index 5256a54167473..e86dad67186f4 100644
--- a/test/functional.jl
+++ b/test/functional.jl
@@ -142,3 +142,45 @@ end
                  for n = 0:5:100-q-d
                  for p = 100-q-d-n
                  if p < n < d < q] == [(50,30,15,5), (50,30,20,0), (50,40,10,0), (75,20,5,0)]
+
+@testset "return type of map() and collect() on generators" begin
+    x = ["a", "b"]
+    res = @inferred collect(s for s in x)
+    @test res isa Vector{String}
+    res = @inferred map(identity, x)
+    @test res isa Vector{String}
+    res = @inferred collect(s === nothing for s in x)
+    @test res isa Vector{Bool}
+    res = @inferred map(s -> s === nothing, x)
+    @test res isa Vector{Bool}
+
+    y = Union{String, Void}["a", nothing]
+    f(::Void) = nothing
+    f(s::String) = s == "a"
+    res = @inferred collect(s for s in y)
+    @test res isa Vector{Union{String, Void}}
+    res = @inferred map(identity, y)
+    @test res isa Vector{Union{String, Void}}
+    res = @inferred collect(s === nothing for s in y)
+    @test res isa Vector{Bool}
+    res = @inferred map(s -> s === nothing, y)
+    @test res isa Vector{Bool}
+    res = @inferred collect(f(s) for s in y)
+    @test res isa Vector{Union{Bool, Void}}
+    res = @inferred map(f, y)
+    @test res isa Vector{Union{Bool, Void}}
+
+    y[2] = "c"
+    res = @inferred collect(s for s in y)
+    @test res isa Vector{Union{String, Void}}
+    res = @inferred map(identity, y)
+    @test res isa Vector{Union{String, Void}}
+    res = @inferred collect(s === nothing for s in y)
+    @test res isa Vector{Bool}
+    res = @inferred map(s -> s === nothing, y)
+    @test res isa Vector{Bool}
+    res = @inferred collect(f(s) for s in y)
+    @test res isa Vector{Union{Bool, Void}}
+    res = @inferred map(f, y)
+    @test res isa Vector{Union{Bool, Void}}
+end