diff --git a/library/proc_macro/src/bridge/client.rs b/library/proc_macro/src/bridge/client.rs
index 60e6950b393..f3582a357ec 100644
--- a/library/proc_macro/src/bridge/client.rs
+++ b/library/proc_macro/src/bridge/client.rs
@@ -49,7 +49,9 @@ macro_rules! define_handles {
             #[repr(C)]
             pub(crate) struct $oty {
                 handle: handle::Handle,
-                // Prevent Send and Sync impls
+                // Prevent Send and Sync impls. `!Send`/`!Sync` is the usual
+                // way of doing this, but that requires unstable features.
+                // rust-analyzer uses this code and avoids unstable features.
                 _marker: PhantomData<*mut ()>,
             }
 
@@ -133,7 +135,9 @@ macro_rules! define_handles {
             #[derive(Copy, Clone, PartialEq, Eq, Hash)]
             pub(crate) struct $ity {
                 handle: handle::Handle,
-                // Prevent Send and Sync impls
+                // Prevent Send and Sync impls. `!Send`/`!Sync` is the usual
+                // way of doing this, but that requires unstable features.
+                // rust-analyzer uses this code and avoids unstable features.
                 _marker: PhantomData<*mut ()>,
             }
 
diff --git a/library/proc_macro/src/bridge/closure.rs b/library/proc_macro/src/bridge/closure.rs
index 06f76d2fc91..d371ae3cea0 100644
--- a/library/proc_macro/src/bridge/closure.rs
+++ b/library/proc_macro/src/bridge/closure.rs
@@ -6,7 +6,11 @@ use std::marker::PhantomData;
 pub struct Closure<'a, A, R> {
     call: unsafe extern "C" fn(*mut Env, A) -> R,
     env: *mut Env,
-    // Ensure Closure is !Send and !Sync
+    // Prevent Send and Sync impls. `!Send`/`!Sync` is the usual way of doing
+    // this, but that requires unstable features. rust-analyzer uses this code
+    // and avoids unstable features.
+    //
+    // The `'a` lifetime parameter represents the lifetime of `Env`.
     _marker: PhantomData<*mut &'a mut ()>,
 }
 
diff --git a/library/proc_macro/src/bridge/mod.rs b/library/proc_macro/src/bridge/mod.rs
index b6b7109135a..c3e4bf1bd6b 100644
--- a/library/proc_macro/src/bridge/mod.rs
+++ b/library/proc_macro/src/bridge/mod.rs
@@ -232,7 +232,9 @@ pub struct Bridge<'a> {
     /// If 'true', always invoke the default panic hook
     force_show_panics: bool,
 
-    // Prevent Send and Sync impls
+    // Prevent Send and Sync impls. `!Send`/`!Sync` is the usual way of doing
+    // this, but that requires unstable features. rust-analyzer uses this code
+    // and avoids unstable features.
     _marker: marker::PhantomData<*mut ()>,
 }