diff --git a/src/tools/compiletest/src/header.rs b/src/tools/compiletest/src/header.rs
index 69658222ff3..3ee315edc51 100644
--- a/src/tools/compiletest/src/header.rs
+++ b/src/tools/compiletest/src/header.rs
@@ -693,6 +693,7 @@ const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "check-run-results",
     "check-stdout",
     "check-test-line-numbers-match",
+    "compare-output-lines-by-subset",
     "compile-flags",
     "dont-check-compiler-stderr",
     "dont-check-compiler-stdout",