diff --git a/crates/rust-analyzer/src/cli/diagnostics.rs b/crates/rust-analyzer/src/cli/diagnostics.rs
index 4006d023def..4306d721298 100644
--- a/crates/rust-analyzer/src/cli/diagnostics.rs
+++ b/crates/rust-analyzer/src/cli/diagnostics.rs
@@ -17,9 +17,15 @@ impl flags::Diagnostics {
     pub fn run(self) -> anyhow::Result<()> {
         let mut cargo_config = CargoConfig::default();
         cargo_config.sysroot = Some(RustLibSource::Discover);
+        let with_proc_macro_server = if let Some(p) = &self.proc_macro_srv {
+            let path = vfs::AbsPathBuf::assert(std::env::current_dir()?.join(&p));
+            ProcMacroServerChoice::Explicit(path)
+        } else {
+            ProcMacroServerChoice::Sysroot
+        };
         let load_cargo_config = LoadCargoConfig {
             load_out_dirs_from_check: !self.disable_build_scripts,
-            with_proc_macro_server: ProcMacroServerChoice::Sysroot,
+            with_proc_macro_server,
             prefill_caches: false,
         };
         let (host, _vfs, _proc_macro) =
diff --git a/crates/rust-analyzer/src/cli/flags.rs b/crates/rust-analyzer/src/cli/flags.rs
index 31012c01b95..c1ca03ceae4 100644
--- a/crates/rust-analyzer/src/cli/flags.rs
+++ b/crates/rust-analyzer/src/cli/flags.rs
@@ -92,6 +92,8 @@
             optional --disable-build-scripts
             /// Don't use expand proc macros.
             optional --disable-proc-macros
+            /// Run a custom proc-macro-srv binary.
+            optional --proc-macro-srv path: PathBuf
         }
 
         cmd ssr {
@@ -189,6 +191,7 @@ pub struct Diagnostics {
 
     pub disable_build_scripts: bool,
     pub disable_proc_macros: bool,
+    pub proc_macro_srv: Option<PathBuf>,
 }
 
 #[derive(Debug)]