diff --git a/onnxscript/function_libs/torch_lib/graph_building.py b/onnxscript/function_libs/torch_lib/graph_building.py
index dc0af0362..057e1a922 100644
--- a/onnxscript/function_libs/torch_lib/graph_building.py
+++ b/onnxscript/function_libs/torch_lib/graph_building.py
@@ -734,6 +734,8 @@ def _add_torchscript_op_call(
     @runtime_typing.checked
     def fetch_opset_imports(self) -> Dict[str, int]:
         # TODO: All local function domain versions are hardcoded as 1.
+        # TODO: Improve the efficiency of this approach.
+        #   This function recursively fetches opset imports from subgraphs.
         opset_imports: Dict[str, int] = {}
         for subgraph in self._sub_torch_script_graphs.values():
             opset_imports.update(subgraph.fetch_opset_imports())
@@ -940,9 +942,9 @@ def to_function_proto(self, opset_version: int, function_name: str) -> onnx.Func
 
         unique_custom_domains = self.fetch_opset_imports()
 
-        while len(onnx_model.opset_import) > 0:
-            opsetid = onnx_model.opset_import.pop()
-            unique_custom_domains[opsetid.domain] = opsetid.version
+        for opset in onnx_model.opset_import:
+            unique_custom_domains[opset.domain] = opset.version
+        del onnx_model.opset_import[:]
         onnx_model.opset_import.extend(
             [
                 onnx.helper.make_opsetid(domain, version)
@@ -1038,9 +1040,9 @@ def to_model_proto(
         # export opset_imports for nested functions, since it does not have access to
         # them. We manually add them back and merge with existing opset_imports in the
         # model proto.
-        while len(onnx_model.opset_import) > 0:
-            opsetid = onnx_model.opset_import.pop()
-            unique_custom_domains[opsetid.domain] = opsetid.version
+        for opset in onnx_model.opset_import:
+            unique_custom_domains[opset.domain] = opset.version
+        del onnx_model.opset_import[:]
         onnx_model.opset_import.extend(
             [
                 onnx.helper.make_opsetid(domain, version)