diff --git a/prost-build/src/config.rs b/prost-build/src/config.rs
index 965d79c7b..c59358246 100644
--- a/prost-build/src/config.rs
+++ b/prost-build/src/config.rs
@@ -1080,7 +1080,7 @@ impl Config {
         let mut modules = HashMap::new();
         let mut packages = HashMap::new();
 
-        let message_graph = MessageGraph::new(requests.iter().map(|x| &x.1));
+        let message_graph = MessageGraph::new(requests.iter().map(|x| &x.1), self.boxed.clone());
         let extern_paths = ExternPaths::new(&self.extern_paths, self.prost_types)
             .map_err(|error| Error::new(ErrorKind::InvalidInput, error))?;
 
diff --git a/prost-build/src/fixtures/field_attributes/_expected_field_attributes.rs b/prost-build/src/fixtures/field_attributes/_expected_field_attributes.rs
index dc420692c..bf1e8c517 100644
--- a/prost-build/src/fixtures/field_attributes/_expected_field_attributes.rs
+++ b/prost-build/src/fixtures/field_attributes/_expected_field_attributes.rs
@@ -19,7 +19,7 @@ pub struct Foo {
     #[prost(string, tag="1")]
     pub foo: ::prost::alloc::string::String,
 }
-#[derive(Clone, Copy, PartialEq, ::prost::Message)]
+#[derive(Clone, PartialEq, ::prost::Message)]
 pub struct Bar {
     #[prost(message, optional, boxed, tag="1")]
     pub qux: ::core::option::Option<::prost::alloc::boxed::Box<Qux>>,
diff --git a/prost-build/src/fixtures/field_attributes/_expected_field_attributes_formatted.rs b/prost-build/src/fixtures/field_attributes/_expected_field_attributes_formatted.rs
index b1955b955..c130aad2e 100644
--- a/prost-build/src/fixtures/field_attributes/_expected_field_attributes_formatted.rs
+++ b/prost-build/src/fixtures/field_attributes/_expected_field_attributes_formatted.rs
@@ -19,7 +19,7 @@ pub struct Foo {
     #[prost(string, tag = "1")]
     pub foo: ::prost::alloc::string::String,
 }
-#[derive(Clone, Copy, PartialEq, ::prost::Message)]
+#[derive(Clone, PartialEq, ::prost::Message)]
 pub struct Bar {
     #[prost(message, optional, boxed, tag = "1")]
     pub qux: ::core::option::Option<::prost::alloc::boxed::Box<Qux>>,
diff --git a/prost-build/src/message_graph.rs b/prost-build/src/message_graph.rs
index 1f02ef352..e2bcad918 100644
--- a/prost-build/src/message_graph.rs
+++ b/prost-build/src/message_graph.rs
@@ -9,6 +9,8 @@ use prost_types::{
     DescriptorProto, FieldDescriptorProto, FileDescriptorProto,
 };
 
+use crate::path::PathMap;
+
 /// `MessageGraph` builds a graph of messages whose edges correspond to nesting.
 /// The goal is to recognize when message types are recursively nested, so
 /// that fields can be boxed when necessary.
@@ -16,14 +18,19 @@ pub struct MessageGraph {
     index: HashMap<String, NodeIndex>,
     graph: Graph<String, ()>,
     messages: HashMap<String, DescriptorProto>,
+    boxed: PathMap<()>,
 }
 
 impl MessageGraph {
-    pub fn new<'a>(files: impl Iterator<Item = &'a FileDescriptorProto>) -> MessageGraph {
+    pub(crate) fn new<'a>(
+        files: impl Iterator<Item = &'a FileDescriptorProto>,
+        boxed: PathMap<()>,
+    ) -> MessageGraph {
         let mut msg_graph = MessageGraph {
             index: HashMap::new(),
             graph: Graph::new(),
             messages: HashMap::new(),
+            boxed,
         };
 
         for file in files {
@@ -74,6 +81,11 @@ impl MessageGraph {
         }
     }
 
+    /// Try get a message descriptor from current message graph
+    pub fn get_message(&self, message: &str) -> Option<&DescriptorProto> {
+        self.messages.get(message)
+    }
+
     /// Returns true if message type `inner` is nested in message type `outer`.
     pub fn is_nested(&self, outer: &str, inner: &str) -> bool {
         let outer = match self.index.get(outer) {
@@ -91,8 +103,9 @@ impl MessageGraph {
     /// Returns `true` if this message can automatically derive Copy trait.
     pub fn can_message_derive_copy(&self, fq_message_name: &str) -> bool {
         assert_eq!(".", &fq_message_name[..1]);
-        let msg = self.messages.get(fq_message_name).unwrap();
-        msg.field
+        self.get_message(fq_message_name)
+            .unwrap()
+            .field
             .iter()
             .all(|field| self.can_field_derive_copy(fq_message_name, field))
     }
@@ -105,10 +118,17 @@ impl MessageGraph {
     ) -> bool {
         assert_eq!(".", &fq_message_name[..1]);
 
+        // repeated field cannot derive Copy
         if field.label() == Label::Repeated {
             false
         } else if field.r#type() == Type::Message {
-            if self.is_nested(field.type_name(), fq_message_name) {
+            // nested and boxed messages cannot derive Copy
+            if self.is_nested(field.type_name(), fq_message_name)
+                || self
+                    .boxed
+                    .get_first_field(fq_message_name, field.name())
+                    .is_some()
+            {
                 false
             } else {
                 self.can_message_derive_copy(field.type_name())
diff --git a/prost-build/src/path.rs b/prost-build/src/path.rs
index f6897005d..2c2d8e242 100644
--- a/prost-build/src/path.rs
+++ b/prost-build/src/path.rs
@@ -3,7 +3,7 @@
 use std::iter;
 
 /// Maps a fully-qualified Protobuf path to a value using path matchers.
-#[derive(Debug, Default)]
+#[derive(Clone, Debug, Default)]
 pub(crate) struct PathMap<T> {
     // insertion order might actually matter (to avoid warning about legacy-derive-helpers)
     // see: https://doc.rust-lang.org/rustc/lints/listing/warn-by-default.html#legacy-derive-helpers