diff --git a/base/deepcopy.jl b/base/deepcopy.jl
index 7ed68bbf2b6acf..5bf1311a13603c 100644
--- a/base/deepcopy.jl
+++ b/base/deepcopy.jl
@@ -27,7 +27,7 @@ updated as appropriate before returning.
 """
 deepcopy(x) = deepcopy_internal(x, IdDict())::typeof(x)
 
-deepcopy_internal(x::Union{Symbol,Core.MethodInstance,Method,GlobalRef,DataType,Union,Task},
+deepcopy_internal(x::Union{Symbol,Core.MethodInstance,Method,GlobalRef,DataType,Union,UnionAll,Task},
                   stackdict::IdDict) = x
 deepcopy_internal(x::Tuple, stackdict::IdDict) =
     ntuple(i->deepcopy_internal(x[i], stackdict), length(x))
diff --git a/test/copy.jl b/test/copy.jl
index 74650d28d42d42..9b7dd82bdf03a9 100644
--- a/test/copy.jl
+++ b/test/copy.jl
@@ -84,6 +84,9 @@ end
     @test c[1] === c[2]
 end
 
+# issue #30911
+@test deepcopy(Array{Int,N} where N) == Array{Int,N} where N
+
 # issue #14027
 struct Nullable14027{T}
     hasvalue::Bool