diff --git a/src/protocol.rs b/src/protocol.rs
index 6b98a971..310fc869 100644
--- a/src/protocol.rs
+++ b/src/protocol.rs
@@ -69,7 +69,7 @@ pub trait Diagnostic: std::error::Error {
     }
 }
 
-macro_rules! box_impls {
+macro_rules! box_error_impls {
     ($($box_type:ty),*) => {
         $(
             impl std::error::Error for $box_type {
@@ -85,12 +85,29 @@ macro_rules! box_impls {
     }
 }
 
-box_impls! {
+box_error_impls! {
     Box<dyn Diagnostic>,
     Box<dyn Diagnostic + Send>,
     Box<dyn Diagnostic + Send + Sync>
 }
 
+macro_rules! box_borrow_impls {
+    ($($box_type:ty),*) => {
+        $(
+            impl std::borrow::Borrow<dyn Diagnostic> for $box_type {
+                fn borrow(&self) -> &(dyn Diagnostic + 'static) {
+                    self.as_ref()
+                }
+            }
+        )*
+    }
+}
+
+box_borrow_impls! {
+    Box<dyn Diagnostic + Send>,
+    Box<dyn Diagnostic + Send + Sync>
+}
+
 impl<T: Diagnostic + Send + Sync + 'static> From<T>
     for Box<dyn Diagnostic + Send + Sync + 'static>
 {
diff --git a/tests/test_diagnostic_source_macro.rs b/tests/test_diagnostic_source_macro.rs
index e5305acd..939812c2 100644
--- a/tests/test_diagnostic_source_macro.rs
+++ b/tests/test_diagnostic_source_macro.rs
@@ -41,6 +41,14 @@ struct TestTupleError(#[diagnostic_source] AnErr);
 #[error("TestError")]
 struct TestBoxedError(#[diagnostic_source] Box<dyn Diagnostic>);
 
+#[derive(Debug, miette::Diagnostic, thiserror::Error)]
+#[error("TestError")]
+struct TestBoxedSendError(#[diagnostic_source] Box<dyn Diagnostic + Send>);
+
+#[derive(Debug, miette::Diagnostic, thiserror::Error)]
+#[error("TestError")]
+struct TestBoxedSendSyncError(#[diagnostic_source] Box<dyn Diagnostic + Send + Sync>);
+
 #[derive(Debug, miette::Diagnostic, thiserror::Error)]
 #[error("TestError")]
 struct TestArcedError(#[diagnostic_source] std::sync::Arc<dyn Diagnostic>);
@@ -71,6 +79,12 @@ fn test_diagnostic_source() {
     let error = TestBoxedError(Box::new(AnErr));
     assert!(error.diagnostic_source().is_some());
 
+    let error = TestBoxedSendError(Box::new(AnErr));
+    assert!(error.diagnostic_source().is_some());
+
+    let error = TestBoxedSendSyncError(Box::new(AnErr));
+    assert!(error.diagnostic_source().is_some());
+
     let error = TestArcedError(std::sync::Arc::new(AnErr));
     assert!(error.diagnostic_source().is_some());
 }