diff --git a/build_system/src/test.rs b/build_system/src/test.rs
index 0895dc6bff7..d39036c26a1 100644
--- a/build_system/src/test.rs
+++ b/build_system/src/test.rs
@@ -703,12 +703,16 @@ fn test_projects(env: &Env, args: &TestArg) -> Result<(), String> {
         //"https://github.com/rust-lang/cargo", // TODO: very slow, only run on master?
     ];
 
+    let mut env = env.clone();
+    let rustflags =
+        format!("{} --cap-lints allow", env.get("RUSTFLAGS").cloned().unwrap_or_default());
+    env.insert("RUSTFLAGS".to_string(), rustflags);
     let run_tests = |projects_path, iter: &mut dyn Iterator<Item = &&str>| -> Result<(), String> {
         for project in iter {
             let clone_result = git_clone_root_dir(project, projects_path, true)?;
             let repo_path = Path::new(&clone_result.repo_dir);
-            run_cargo_command(&[&"build", &"--release"], Some(repo_path), env, args)?;
-            run_cargo_command(&[&"test"], Some(repo_path), env, args)?;
+            run_cargo_command(&[&"build", &"--release"], Some(repo_path), &env, args)?;
+            run_cargo_command(&[&"test"], Some(repo_path), &env, args)?;
         }
 
         Ok(())