diff --git a/TypedSyntax/src/show.jl b/TypedSyntax/src/show.jl
index 79361ca5..d1965f95 100644
--- a/TypedSyntax/src/show.jl
+++ b/TypedSyntax/src/show.jl
@@ -99,7 +99,7 @@ function type_annotation_mode(node, @nospecialize(T); type_annotations::Bool, hi
     type_annotate = is_show_annotation(T; type_annotations, hide_type_stable)
     pre = pre2 = post = ""
     if type_annotate
-        if T isa Type && T <: Type
+        if T isa Type && T <: Type && T !== Union{} && isassigned(T.parameters, 1)
             # Don't annotate `String::Type{String}`
             if replace(sourcetext(node), r"\s" => "") == replace(sprint(show, T.parameters[1]), r"\s" => "")
                 return false, pre, pre2, post
diff --git a/TypedSyntax/test/runtests.jl b/TypedSyntax/test/runtests.jl
index bc880f3a..c192744d 100644
--- a/TypedSyntax/test/runtests.jl
+++ b/TypedSyntax/test/runtests.jl
@@ -650,6 +650,16 @@ include("test_module.jl")
     @test_nowarn str = sprint(tsn; context=:color=>false) do io, obj
         printstyled(io, obj; hide_type_stable=false)
     end
+
+    # issue 491
+    tsn = TypedSyntaxNode(+, (Int, Int)) # need a node, not important what it is
+    @test_nowarn TypedSyntax.type_annotation_mode(tsn, Union{}; type_annotations=true, hide_type_stable=false)
+
+    # issue 492
+    tsn = TypedSyntaxNode(Base._tuple_unique_fieldtypes, (Any,))
+    @test_nowarn str = sprint(tsn; context=:color=>false) do io, obj
+        printstyled(io, obj; hide_type_stable=false)
+    end
 end
 
 if parse(Bool, get(ENV, "CI", "false"))