diff --git a/base/broadcast.jl b/base/broadcast.jl
index b89826bb22bb39..cb23f6523ac2ff 100644
--- a/base/broadcast.jl
+++ b/base/broadcast.jl
@@ -314,9 +314,8 @@ some cases.
 """
 function flatten(bc::Broadcasted{Style}) where {Style}
     isflat(bc) && return bc
-    # concatenate the nested arguments into {a, b, c, d}
-    # args = cat_nested(bc)
-    # build a function `makeargs` that takes a "flat" argument list and
+    # 1. concatenate the nested arguments into {a, b, c, d}
+    # 2. build a function `makeargs` that takes a "flat" argument list and
     # and creates the appropriate input arguments for `f`, e.g.,
     #          makeargs = (w, x, y, z) -> (w, g(x, y), z)
     #
@@ -329,8 +328,7 @@ function flatten(bc::Broadcasted{Style}) where {Style}
             @inline function (args::Vararg{Any,N})
                 f(makeargs(args...)...)
             end
-        newf = _make(args)
-        return Broadcasted{Style}(newf, args, bc.axes)
+        return Broadcasted{Style}(_make(args), args, bc.axes)
     end
 end
 
@@ -340,18 +338,13 @@ _isflat(args::NestedTuple) = false
 _isflat(args::Tuple) = _isflat(tail(args))
 _isflat(args::Tuple{}) = true
 
-cat_nested(t::Broadcasted, rest...) = (cat_nested(t.args...)..., cat_nested(rest...)...)
-cat_nested(t::Any, rest...) = (t, cat_nested(rest...)...)
-cat_nested() = ()
-
 """
     make_makeargs(args::Tuple, t::Tuple) -> Function, Tuple
 
 Each element of `t` is one (consecutive) node in a broadcast tree.
 `args` contains the rest arguments on the "right" side of `t`.
 The jobs of `make_makeargs` are:
-    1. append the flattened arguments in `t` at the beginning of `args`, i.e.
-    `(cat_nested(t)..., args...)`
+    1. append the flattened arguments in `t` at the beginning of `args`.
     2. return a function that takes in flattened argument list and returns a
     tuple (each entry corresponding to an entry in `t`, having evaluated
     the corresponding element in the broadcast tree).
diff --git a/test/broadcast.jl b/test/broadcast.jl
index 18534c6bab4e76..c17c90b21ded91 100644
--- a/test/broadcast.jl
+++ b/test/broadcast.jl
@@ -772,16 +772,19 @@ end
 
 # issue #27988: inference of Broadcast.flatten
 using .Broadcast: Broadcasted
-let
+let _cat_nested(bc) = Broadcast.flatten(bc).args
     bc = Broadcasted(+, (Broadcasted(*, (1, 2)), Broadcasted(*, (Broadcasted(*, (3, 4)), 5))))
-    @test @inferred(Broadcast.cat_nested(bc)) == (1,2,3,4,5)
+    @test @inferred(_cat_nested(bc)) == (1,2,3,4,5)
     @test @inferred(Broadcast.materialize(Broadcast.flatten(bc))) == @inferred(Broadcast.materialize(bc)) == 62
     bc = Broadcasted(+, (Broadcasted(*, (1, Broadcasted(/, (2.0, 2.5)))), Broadcasted(*, (Broadcasted(*, (3, 4)), 5))))
-    @test @inferred(Broadcast.cat_nested(bc)) == (1,2.0,2.5,3,4,5)
+    @test @inferred(_cat_nested(bc)) == (1,2.0,2.5,3,4,5)
     @test @inferred(Broadcast.materialize(Broadcast.flatten(bc))) == @inferred(Broadcast.materialize(bc)) == 60.8
     # 1 .* 1 .- 1 .* 1 .^2 .+ 1 .* 1 .+ 1 .^ 3
-    bc = Base.Broadcast.Broadcasted(+, (Base.Broadcast.Broadcasted(+, (Base.Broadcast.Broadcasted(-, (Base.Broadcast.Broadcasted(*, (1, 1)), Base.Broadcast.Broadcasted(*, (1, Base.Broadcast.Broadcasted(Base.literal_pow, (Base.RefValue{typeof(^)}(^), 1, Base.RefValue{Val{2}}(Val{2}()))))))), Base.Broadcast.Broadcasted(*, (1, 1)))), Base.Broadcast.Broadcasted(Base.literal_pow, (Base.RefValue{typeof(^)}(^), 1, Base.RefValue{Val{3}}(Val{3}())))))
+    bc = Broadcasted(+, (Broadcasted(+, (Broadcasted(-, (Broadcasted(*, (1, 1)), Broadcasted(*, (1, Broadcasted(Base.literal_pow, (Ref(^), 1, Ref(Val(2)))))))), Broadcasted(*, (1, 1)))), Broadcasted(Base.literal_pow, (Base.RefValue{typeof(^)}(^), 1, Base.RefValue{Val{3}}(Val{3}())))))
     @test @inferred(Broadcast.materialize(Broadcast.flatten(bc))) == @inferred(Broadcast.materialize(bc)) == 2
+    # @. 1 + 1 * (1 + 1 + 1 + 1)
+    bc = Broadcasted(+, (1, Broadcasted(*, (1, Broadcasted(+, (1, 1, 1, 1))))))
+    @test @inferred(_cat_nested(bc)) == (1,1,1,1,1,1) # `cat_nested` failed to infer this
 end
 
 let