diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 3c85b9076dd1..727eecbb7325 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -1452,6 +1452,8 @@ impl<'test> TestCx<'test> {
             .arg(aux_dir)
             .arg("-o")
             .arg(out_dir)
+            .arg("--deny")
+            .arg("warnings")
             .arg(&self.testpaths.file)
             .args(&self.props.compile_flags);