diff --git a/tests/compiletest.rs b/tests/compiletest.rs
index 9394084ad34d..eaf7f8531b8f 100644
--- a/tests/compiletest.rs
+++ b/tests/compiletest.rs
@@ -25,9 +25,14 @@ fn rustc_lib_path() -> PathBuf {
 }
 
 fn run_tests(mode: &str, path: &str, target: &str, mut flags: Vec<String>) {
-    // Some flags we always want.
-    flags.push("-Dwarnings -Dunused".to_owned()); // overwrite the -Aunused in compiletest-rs
+    let in_rustc_test_suite = rustc_test_suite().is_some();
+    // Add some flags we always want.
     flags.push("--edition 2018".to_owned());
+    if !in_rustc_test_suite {
+      // Only `-Dwarnings` on the Miri side to make the rustc toolstate management less painful.
+      // (We often get warnings when e.g. a feature gets stabilized or some lint gets added/improved.)
+      flags.push("-Dwarnings -Dunused".to_owned()); // overwrite the -Aunused in compiletest-rs
+    }
     if let Ok(sysroot) = std::env::var("MIRI_SYSROOT") {
         flags.push(format!("--sysroot {}", sysroot));
     }
@@ -36,7 +41,7 @@ fn run_tests(mode: &str, path: &str, target: &str, mut flags: Vec<String>) {
     let mut config = compiletest::Config::default().tempdir();
     config.mode = mode.parse().expect("Invalid mode");
     config.rustc_path = miri_path();
-    if rustc_test_suite().is_some() {
+    if in_rustc_test_suite {
         config.run_lib_path = rustc_lib_path();
         config.compile_lib_path = rustc_lib_path();
     }