diff --git a/onnxruntime/core/graph/graph.cc b/onnxruntime/core/graph/graph.cc
index eb5ab3e8f1371..baebe2420073b 100644
--- a/onnxruntime/core/graph/graph.cc
+++ b/onnxruntime/core/graph/graph.cc
@@ -622,19 +622,6 @@ bool Node::TryGetFunctionProto(ONNX_NAMESPACE::FunctionProto& onnx_function_prot
       // non-onnx domains, like MSDOMAIN.
 
       auto requested_opset_version = get_opset_version(graph_);
-
-      /// When we fix custom function registration then we can apply the following
-      /// logic for non ONNX domains as we do for ONNX. Currently, we only apply ONNX
-      /// domain version
-      /* {
-        const auto iter = domain_to_version.find(op_->domain());
-        if (iter != domain_to_version.cend()) {
-          function_ptr = op_->GetFunction(iter->second, true);
-        } else {
-          function_ptr = op_->GetFunction();
-        }
-      }*/
-
       if (requested_opset_version.has_value()) {
         function_ptr = op_->GetFunction(*requested_opset_version, true);
       } else {
diff --git a/onnxruntime/test/framework/function_test.cc b/onnxruntime/test/framework/function_test.cc
index 9ab78cac3aca4..956477a0e92bb 100644
--- a/onnxruntime/test/framework/function_test.cc
+++ b/onnxruntime/test/framework/function_test.cc
@@ -614,5 +614,59 @@ TEST(FunctionTest, TestInlinedFunctionDoesNotReserrectNonExistingArgs) {
                                       AsSpan(output_names), &fetches, 0));
 }
 
+/// <summary>
+/// This test covers the issues:
+/// https://github.com/microsoft/onnxruntime/issues/16438
+/// https://github.com/microsoft/onnxruntime/issues/18781
+/// </summary>
+TEST(FunctionTest, Test_GH_issue_16438) {
+  const char* code = R"(
+    <
+       ir_version: 8,
+       opset_import: ["pkg.onnxscript.torch_lib" : 1, "" : 18],
+       producer_name: "pytorch",
+       producer_version: "2.1.0"
+    >
+    torch_jit (float16[5,10,5] input_0) => (double[5,10,5] _val_1) {
+       _val_1 = pkg.onnxscript.torch_lib.aten_special_log_softmax <dim: int = 2, dtype: int = 11> (input_0)
+    }
+    <
+      domain: "pkg.onnxscript.torch_lib",
+      opset_import: ["" : 18]
+    >
+    aten_special_log_softmax <dim, dtype>(self) => (result_8)
+    {
+      tmp = Shape(self)
+      tmp_0 = Size(tmp)
+      int64_0 = Constant<value : tensor = int64 int64_0{0}> ()
+      int64_0_cast = CastLike(int64_0, tmp_0)
+      self_is_scalar = Equal(tmp_0, int64_0_cast)
+      self_4 = If(self_is_scalar) <then_branch : graph = thenGraph_8() => (self_2) {
+        tmp_1 = Constant<value_ints : ints = [0]> ()
+        self_2 = Unsqueeze(self, tmp_1)
+      }, else_branch : graph = elseGraph_8() => (self_3) {
+        self_3 = Identity(self)
+      }>
+      result = LogSoftmax<axis : int = @dim>(self_4)
+      result_5 = Cast<to : int = @dtype>(result)
+      result_8 = If(self_is_scalar) <then_branch : graph = thenGraph_12() => (result_6) {
+       result_6 = Squeeze(result_5)
+      }, else_branch : graph = elseGraph_12() => (result_7) {
+        result_7 = Identity(result_5)
+      }>
+    }
+  )";
+  
+  std::string serialized_model;
+  ParseOnnxSource(code, serialized_model);
+  SessionOptions session_options;
+  InferenceSession session_object{session_options, GetEnvironment()};
+
+  std::stringstream sstr(serialized_model);
+  auto status = session_object.Load(sstr);
+  ASSERT_TRUE(status.IsOK()) << status.ErrorMessage();
+  status = session_object.Initialize();
+  ASSERT_TRUE(status.IsOK()) << status.ErrorMessage();
+}
 }  // namespace test
 }  // namespace onnxruntime