diff --git a/src/tools/compiletest/src/directive-list.rs b/src/tools/compiletest/src/directive-list.rs
index 952533e904c5a..f3f769714641a 100644
--- a/src/tools/compiletest/src/directive-list.rs
+++ b/src/tools/compiletest/src/directive-list.rs
@@ -17,7 +17,6 @@ const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "check-run-results",
     "check-stdout",
     "check-test-line-numbers-match",
-    "compare-output-lines-by-subset",
     "compile-flags",
     "doc-flags",
     "dont-check-compiler-stderr",
diff --git a/src/tools/compiletest/src/header.rs b/src/tools/compiletest/src/header.rs
index fe4c5fdd8b51c..73e56cfac8f68 100644
--- a/src/tools/compiletest/src/header.rs
+++ b/src/tools/compiletest/src/header.rs
@@ -115,9 +115,6 @@ pub struct TestProps {
     pub dont_check_compiler_stdout: bool,
     // For UI tests, allows compiler to generate arbitrary output to stderr
     pub dont_check_compiler_stderr: bool,
-    // When checking the output of stdout or stderr check
-    // that the lines of expected output are a subset of the actual output.
-    pub compare_output_lines_by_subset: bool,
     // Don't force a --crate-type=dylib flag on the command line
     //
     // Set this for example if you have an auxiliary test file that contains
@@ -240,7 +237,6 @@ mod directives {
     pub const KNOWN_BUG: &'static str = "known-bug";
     pub const TEST_MIR_PASS: &'static str = "test-mir-pass";
     pub const REMAP_SRC_BASE: &'static str = "remap-src-base";
-    pub const COMPARE_OUTPUT_LINES_BY_SUBSET: &'static str = "compare-output-lines-by-subset";
     pub const LLVM_COV_FLAGS: &'static str = "llvm-cov-flags";
     pub const FILECHECK_FLAGS: &'static str = "filecheck-flags";
     pub const NO_AUTO_CHECK_CFG: &'static str = "no-auto-check-cfg";
@@ -274,7 +270,6 @@ impl TestProps {
             check_run_results: false,
             dont_check_compiler_stdout: false,
             dont_check_compiler_stderr: false,
-            compare_output_lines_by_subset: false,
             no_prefer_dynamic: false,
             pretty_mode: "normal".to_string(),
             pretty_compare_only: false,
@@ -550,11 +545,6 @@ impl TestProps {
                         |s| s.trim().to_string(),
                     );
                     config.set_name_directive(ln, REMAP_SRC_BASE, &mut self.remap_src_base);
-                    config.set_name_directive(
-                        ln,
-                        COMPARE_OUTPUT_LINES_BY_SUBSET,
-                        &mut self.compare_output_lines_by_subset,
-                    );
 
                     if let Some(flags) = config.parse_name_value_directive(ln, LLVM_COV_FLAGS) {
                         self.llvm_cov_flags.extend(split_flags(&flags));
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 93e5980f1f5fb..7be9e2f2d5772 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -2541,13 +2541,10 @@ impl<'test> TestCx<'test> {
             return 0;
         }
 
-        // If `compare-output-lines-by-subset` is not explicitly enabled then
-        // auto-enable it when a `runner` is in use since wrapper tools might
-        // provide extra output on failure, for example a WebAssembly runtime
-        // might print the stack trace of an `unreachable` instruction by
-        // default.
-        let compare_output_by_lines =
-            self.props.compare_output_lines_by_subset || self.config.runner.is_some();
+        // Wrapper tools set by `runner` might provide extra output on failure,
+        // for example a WebAssembly runtime might print the stack trace of an
+        // `unreachable` instruction by default.
+        let compare_output_by_lines = self.config.runner.is_some();
 
         let tmp;
         let (expected, actual): (&str, &str) = if compare_output_by_lines {