diff --git a/prost-build/src/code_generator.rs b/prost-build/src/code_generator.rs
index 7fa181765..1ab19ee41 100644
--- a/prost-build/src/code_generator.rs
+++ b/prost-build/src/code_generator.rs
@@ -367,7 +367,7 @@ impl<'a> CodeGenerator<'a> {
         let repeated = field.label == Some(Label::Repeated as i32);
         let deprecated = self.deprecated(&field);
         let optional = self.optional(&field);
-        let boxed = self.boxed(&field, fq_message_name);
+        let boxed = self.boxed(&field, fq_message_name, None);
         let ty = self.resolve_type(&field, fq_message_name);
 
         debug!(
@@ -576,9 +576,9 @@ impl<'a> CodeGenerator<'a> {
         self.path.pop();
         self.path.pop();
 
-        let oneof_name = format!("{}.{}", fq_message_name, oneof.name());
-        self.append_type_attributes(&oneof_name);
-        self.append_enum_attributes(&oneof_name);
+        let fq_oneof_name = format!("{}.{}", fq_message_name, oneof.name());
+        self.append_type_attributes(&fq_oneof_name);
+        self.append_enum_attributes(&fq_oneof_name);
         self.push_indent();
         self.buf
             .push_str("#[allow(clippy::derive_partial_eq_without_eq)]\n");
@@ -595,8 +595,6 @@ impl<'a> CodeGenerator<'a> {
         self.path.push(2);
         self.depth += 1;
         for (field, idx) in fields {
-            let type_ = field.r#type();
-
             self.path.push(idx as i32);
             self.append_doc(fq_message_name, Some(field.name()));
             self.path.pop();
@@ -608,20 +606,12 @@ impl<'a> CodeGenerator<'a> {
                 ty_tag,
                 field.number()
             ));
-            self.append_field_attributes(&oneof_name, field.name());
+            self.append_field_attributes(&fq_oneof_name, field.name());
 
             self.push_indent();
             let ty = self.resolve_type(&field, fq_message_name);
 
-            let boxed = ((type_ == Type::Message || type_ == Type::Group)
-                && self
-                    .message_graph
-                    .is_nested(field.type_name(), fq_message_name))
-                || (self
-                    .config
-                    .boxed
-                    .get_first_field(&oneof_name, field.name())
-                    .is_some());
+            let boxed = self.boxed(&field, fq_message_name, Some(oneof.name()));
 
             debug!(
                 "    oneof: {:?}, type: {:?}, boxed: {}",
@@ -1026,18 +1016,31 @@ impl<'a> CodeGenerator<'a> {
         }
     }
 
-    fn boxed(&self, field: &FieldDescriptorProto, fq_message_name: &str) -> bool {
+    fn boxed(
+        &self,
+        field: &FieldDescriptorProto,
+        fq_message_name: &str,
+        oneof: Option<&str>,
+    ) -> bool {
+        if field.label == Some(Label::Repeated as i32) {
+            return false;
+        }
         let fd_type = field.r#type();
-        field.label != Some(Label::Repeated as i32)
-            && ((fd_type == Type::Message || fd_type == Type::Group)
-                && self
-                    .message_graph
-                    .is_nested(field.type_name(), fq_message_name))
-            || (self
-                .config
-                .boxed
-                .get_first_field(fq_message_name, field.name())
-                .is_some())
+        if (fd_type == Type::Message || fd_type == Type::Group)
+            && self
+                .message_graph
+                .is_nested(field.type_name(), fq_message_name)
+        {
+            return true;
+        }
+        let config_path = match oneof {
+            None => Cow::Borrowed(fq_message_name),
+            Some(ooname) => Cow::Owned(format!("{fq_message_name}.{ooname}")),
+        };
+        self.config
+            .boxed
+            .get_first_field(&config_path, field.name())
+            .is_some()
     }
 
     /// Returns `true` if the field options includes the `deprecated` option.