--- a/build/config/rust.gni
+++ b/build/config/rust.gni
@@ -58,3 +58,6 @@
   rust_sysroot_absolute = ""
+
+  # Use a system Crubit built against the selected Rust compiler.
+  use_system_crubit = false

   # Directory under which to find `bin/bindgen` (a `bin` directory containing
@@ -130,1 +130,1 @@
-use_chromium_rust_toolchain = rust_sysroot_absolute == ""
+use_chromium_rust_toolchain = rust_sysroot_absolute == "" || use_system_crubit
@@ -427,1 +427,1 @@
-enable_cpp_api_from_rust = enable_rust && use_chromium_rust_toolchain &&
+enable_cpp_api_from_rust = enable_rust && (use_chromium_rust_toolchain || use_system_crubit) &&
--- a/build/rust/gni_impl/cpp_api_from_rust.gni
+++ b/build/rust/gni_impl/cpp_api_from_rust.gni
@@ -49,1 +49,1 @@
-  assert(enable_rust && use_chromium_rust_toolchain)
+  assert(enable_rust && (use_chromium_rust_toolchain || use_system_crubit))