diff --git a/pb-jelly-gen/codegen/codegen.py b/pb-jelly-gen/codegen/codegen.py
index 762c1d7..7b13d46 100755
--- a/pb-jelly-gen/codegen/codegen.py
+++ b/pb-jelly-gen/codegen/codegen.py
@@ -276,6 +276,8 @@ def custom_type(self) -> Text:
         return self.field.options.Extensions[extensions_pb2.type]
 
     def is_nullable(self) -> bool:
+        if self.oneof:
+            return False
         if (
             self.field.type in PRIMITIVE_TYPES
             and self.is_proto3
@@ -362,7 +364,7 @@ def set_method(self) -> Tuple[Text, Text]:
         elif self.field.type == FieldDescriptorProto.TYPE_ENUM:
             return self.rust_type(), "v"
         elif self.field.type == FieldDescriptorProto.TYPE_MESSAGE:
-            return self.rust_type(maybe_boxed=True), "v"
+            return self.storage_type(), "v"
         raise AssertionError("Unexpected field type")
 
     def take_method(self) -> Tuple[Optional[Text], Optional[Text]]:
@@ -395,7 +397,7 @@ def take_method(self) -> Tuple[Optional[Text], Optional[Text]]:
         elif self.field.type == FieldDescriptorProto.TYPE_ENUM:
             return self.rust_type(), expr
         elif self.field.type == FieldDescriptorProto.TYPE_MESSAGE:
-            return self.rust_type(maybe_boxed=True), expr
+            return self.storage_type(), expr
         raise AssertionError("Unexpected field type")
 
     def get_method(self) -> Tuple[Text, Text]:
@@ -446,10 +448,7 @@ def get_method(self) -> Tuple[Text, Text]:
             )
         raise AssertionError("Unexpected field type")
 
-    def rust_type(self, maybe_boxed: bool = False) -> Text:
-        if maybe_boxed and self.is_boxed():
-            return "::std::boxed::Box<%s>" % self.rust_type(maybe_boxed=False)
-
+    def rust_type(self) -> Text:
         typ = self.field.type
 
         if self.has_custom_type():
@@ -485,15 +484,18 @@ def rust_type(self, maybe_boxed: bool = False) -> Text:
             "Unsupported type: {!r}".format(FieldDescriptorProto.Type.Name(typ))
         )
 
-    def __str__(self) -> str:
-        rust_type = self.rust_type(maybe_boxed=True)
+    def storage_type(self) -> str:
+        rust_type = self.rust_type()
+
+        if self.is_boxed():
+            rust_type = "::std::boxed::Box<%s>" % rust_type
 
         if self.is_repeated():
-            return "::std::vec::Vec<%s>" % rust_type
+            rust_type = "::std::vec::Vec<%s>" % rust_type
         elif self.is_nullable():
-            return "::std::option::Option<%s>" % rust_type
-        else:
-            return rust_type
+            rust_type = "::std::option::Option<%s>" % rust_type
+
+        return rust_type
 
     def oneof_field_match(self, var: Text) -> Text:
         if self.is_empty_oneof_field():
@@ -931,7 +933,7 @@ def gen_msg(
                 if typ.oneof:
                     oneof_fields[typ.oneof.name].append(field)
                 else:
-                    self.write("pub %s: %s," % (field.name, typ))
+                    self.write("pub %s: %s," % (field.name, typ.storage_type()))
 
             for oneof in oneof_decls:
                 if oneof_nullable(oneof):
@@ -954,7 +956,7 @@ def gen_msg(
                 for oneof_field in oneof_fields[oneof.name]:
                     typ = self.rust_type(msg_type, oneof_field)
                     self.write(
-                        "%s," % typ.oneof_field_match(typ.rust_type(maybe_boxed=True))
+                        "%s," % typ.oneof_field_match(typ.storage_type())
                     )
 
         if not self.is_proto3: