diff --git a/src/subtype.c b/src/subtype.c
index 39211fcf55d2d..b89574c315496 100644
--- a/src/subtype.c
+++ b/src/subtype.c
@@ -4439,7 +4439,7 @@ static jl_value_t *insert_nondiagonal(jl_value_t *type, jl_varbinding_t *troot,
         newa = insert_nondiagonal(a, troot, widen2ub);
         newb = insert_nondiagonal(b, troot, widen2ub);
         if (newa != a || newb != b)
-            type = (jl_value_t *)jl_new_struct(jl_uniontype_type, newa, newb);
+            type = simple_union(newa, newb);
         JL_GC_POP();
     }
     else if (jl_is_vararg(type)) {
@@ -4499,7 +4499,8 @@ static jl_value_t *widen_diagonal(jl_value_t *t, jl_unionall_t *u, jl_varbinding
     if (vb.innervars != NULL) {
         for (size_t i = 0; i < jl_array_nrows(vb.innervars); i++) {
             jl_tvar_t *var = (jl_tvar_t*)jl_array_ptr_ref(vb.innervars, i);
-            nt = jl_type_unionall(var, nt);
+            if (jl_has_typevar(nt, var))
+                nt = jl_type_unionall(var, nt);
         }
     }
     JL_GC_POP();
diff --git a/test/core.jl b/test/core.jl
index df799b0abf42d..7cd4be5427eb4 100644
--- a/test/core.jl
+++ b/test/core.jl
@@ -8067,5 +8067,6 @@ let widen_diagonal(x::UnionAll) = Base.rewrap_unionall(Base.widen_diagonal(Base.
     @test Tuple{Int,Float64} <: widen_diagonal(Tuple{T,T} where {T})
     @test Tuple{Real,Int,Float64} <: widen_diagonal(Tuple{S,Vararg{T}} where {S, T<:S})
     @test Tuple{Int,Int,Float64,Float64} <: widen_diagonal(Tuple{S,S,Vararg{T}} where {S, T<:S})
-    @test Union{Tuple{T}, Tuple{T,Int}} where {T} == widen_diagonal(Union{Tuple{T}, Tuple{T,Int}} where {T})
+    @test Union{Tuple{T}, Tuple{T,Int}} where {T} === widen_diagonal(Union{Tuple{T}, Tuple{T,Int}} where {T})
+    @test Tuple === widen_diagonal(Union{Tuple{Vararg{S}}, Tuple{Vararg{T}}} where {S, T})
 end