diff --git a/lib/typeprof/core/ast/misc.rb b/lib/typeprof/core/ast/misc.rb
index 9c94bc5e..52db028d 100644
--- a/lib/typeprof/core/ast/misc.rb
+++ b/lib/typeprof/core/ast/misc.rb
@@ -256,9 +256,9 @@ def install0(genv)
         vtx = @expr.install(genv)
 
         a_args = ActualArguments.new([], [], nil, nil)
-        vtx = @changes.add_method_call_box(genv, vtx, :to_a, a_args, false).ret
+        to_a_vtx = @changes.add_method_call_box(genv, vtx, :to_a, a_args, false, suppress_errors: true).ret
 
-        @changes.add_splat_box(genv, vtx).ret
+        @changes.add_splat_box(genv, to_a_vtx, nil, vtx).ret
       end
     end
 
diff --git a/lib/typeprof/core/graph/box.rb b/lib/typeprof/core/graph/box.rb
index 1e62042c..91fb388d 100644
--- a/lib/typeprof/core/graph/box.rb
+++ b/lib/typeprof/core/graph/box.rb
@@ -600,11 +600,13 @@ def wrong_return_type(f_ret_show, changes)
   end
 
   class SplatBox < Box
-    def initialize(node, genv, ary, idx)
+    def initialize(node, genv, ary, idx, orig = nil)
       super(node)
       @ary = ary
       @idx = idx
+      @orig = orig
       @ary.add_edge(genv, self)
+      @orig.add_edge(genv, self) if @orig
       @ret = Vertex.new(node)
     end
 
@@ -629,6 +631,12 @@ def run0(genv, changes)
           "???"
         end
       end
+      # For types where to_a is not defined, [*x] wraps x as [x]
+      if @orig && @ary.types.empty?
+        @orig.each_type do |ty|
+          changes.add_edge(genv, Source.new(ty), @ret)
+        end
+      end
     end
   end
 
@@ -992,7 +1000,7 @@ def run0(genv, changes)
   end
 
   class MethodCallBox < Box
-    def initialize(node, genv, recv, mid, a_args, subclasses)
+    def initialize(node, genv, recv, mid, a_args, subclasses, suppress_errors: false)
       raise mid.to_s unless mid
       super(node)
       @recv = recv.new_vertex(genv, node)
@@ -1003,6 +1011,7 @@ def initialize(node, genv, recv, mid, a_args, subclasses)
       @a_args.block.add_edge(genv, self) if @a_args.block
       @ret = Vertex.new(node)
       @subclasses = subclasses
+      @suppress_errors = suppress_errors
       @generics = {}
     end
 
@@ -1014,10 +1023,11 @@ def run0(genv, changes)
       error_count = 0
       resolve(genv, changes) do |me, ty, mid, orig_ty|
         if !me
-          # TODO: undefined method error
-          if error_count < 3
-            meth = @node.mid_code_range ? :mid_code_range : :code_range
-            changes.add_diagnostic(meth, "undefined method: #{ orig_ty.show }##{ mid }")
+          unless @suppress_errors
+            if error_count < 3
+              meth = @node.mid_code_range ? :mid_code_range : :code_range
+              changes.add_diagnostic(meth, "undefined method: #{ orig_ty.show }##{ mid }")
+            end
           end
           error_count += 1
         elsif me.builtin && me.builtin[changes, @node, orig_ty, @a_args, @ret]
@@ -1062,7 +1072,7 @@ def run0(genv, changes)
       edges.each do |src, dst|
         changes.add_edge(genv, src, dst)
       end
-      if error_count > 3
+      if error_count > 3 && !@suppress_errors
         meth = @node.mid_code_range ? :mid_code_range : :code_range
         changes.add_diagnostic(meth, "... and other #{ error_count - 3 } errors")
       end
diff --git a/lib/typeprof/core/graph/change_set.rb b/lib/typeprof/core/graph/change_set.rb
index 802d864a..57bada27 100644
--- a/lib/typeprof/core/graph/change_set.rb
+++ b/lib/typeprof/core/graph/change_set.rb
@@ -69,9 +69,9 @@ def add_edge(genv, src, dst)
 
     # TODO: if an edge is removed during one analysis, we may need to remove sub-boxes?
 
-    def add_method_call_box(genv, recv, mid, a_args, subclasses)
-      key = [:mcall, recv, mid, a_args, subclasses]
-      @new_boxes[key] ||= MethodCallBox.new(@node, genv, recv, mid, a_args, subclasses)
+    def add_method_call_box(genv, recv, mid, a_args, subclasses, suppress_errors: false)
+      key = [:mcall, recv, mid, a_args, subclasses, suppress_errors]
+      @new_boxes[key] ||= MethodCallBox.new(@node, genv, recv, mid, a_args, subclasses, suppress_errors: suppress_errors)
     end
 
     def add_escape_box(genv, a_ret)
@@ -79,9 +79,9 @@ def add_escape_box(genv, a_ret)
       @new_boxes[key] ||= EscapeBox.new(@node, genv, a_ret)
     end
 
-    def add_splat_box(genv, arg, idx = nil)
-      key = [:splat, arg, idx]
-      @new_boxes[key] ||= SplatBox.new(@node, genv, arg, idx)
+    def add_splat_box(genv, arg, idx = nil, orig = nil)
+      key = [:splat, arg, idx, orig]
+      @new_boxes[key] ||= SplatBox.new(@node, genv, arg, idx, orig)
     end
 
     def add_hash_splat_box(genv, arg, unified_key, unified_val)
diff --git a/scenario/known-issues/splat-union-fallback.rb b/scenario/known-issues/splat-union-fallback.rb
new file mode 100644
index 00000000..a6b6b625
--- /dev/null
+++ b/scenario/known-issues/splat-union-fallback.rb
@@ -0,0 +1,12 @@
+## update
+def foo(x)
+  [*x]
+end
+
+foo([:int])
+foo(:sym)
+
+## assert
+class Object
+  def foo: (Array[:int] | :sym) -> Array[:int | :sym]
+end