diff --git a/ariadne_codegen/client_generators/custom_arguments.py b/ariadne_codegen/client_generators/custom_arguments.py
index 0841a02..5f8a2a5 100644
--- a/ariadne_codegen/client_generators/custom_arguments.py
+++ b/ariadne_codegen/client_generators/custom_arguments.py
@@ -94,7 +94,6 @@ def generate_arguments(
                 arg_name,
                 name,
                 final_type,
-                is_required,
                 used_custom_scalar,
             )
 
@@ -125,12 +124,11 @@ def _accumulate_return_arguments(
         return_arguments_values: List[ast.expr],
         arg_name: str,
         name: str,
-        final_type: Union[GraphQLObjectType, GraphQLInterfaceType, GraphQLUnionType],
-        is_required: bool,
+        final_type: Union[GraphQLObjectType, GraphQLInterfaceType, GraphQLUnionType]
         used_custom_scalar: Optional[str],
     ) -> None:
         """Accumulates return arguments."""
-        constant_value = f"{final_type.name}!" if is_required else final_type.name
+        constant_value = self._generate_complete_type_name(complete_type)
         return_arg_dict_value = self._generate_return_arg_value(
             name, used_custom_scalar
         )
@@ -143,6 +141,22 @@ def _accumulate_return_arguments(
             )
         )
 
+    def _generate_complete_type_name(
+        self, 
+        complete_type: Union[GraphQLObjectType, GraphQLInterfaceType, GraphQLUnionType, GraphQLNonNull, GraphQLList]
+    ) -> str:
+        if isinstance(complete_type, GraphQLNonNull):
+            if hasattr(complete_type, "of_type"):
+                return f"{self._generate_complete_type_name(complete_type.of_type)}!"
+            else:
+                return f"{self._generate_complete_type_name(complete_type.type)}"
+        if isinstance(complete_type, GraphQLList):
+            if hasattr(complete_type, "of_type"):
+                return f"[{self._generate_complete_type_name(complete_type.of_type)}]"
+            else:
+                return f"[{self._generate_complete_type_name(complete_type.type)}]"
+        return complete_type.name
+    
     def _generate_return_arg_value(
         self, name: str, used_custom_scalar: Optional[str]
     ) -> Union[ast.Call, ast.Name]: