diff --git a/lib/internal/test_runner/test.js b/lib/internal/test_runner/test.js
index a2391047138bd9..ffbf2d257aed62 100644
--- a/lib/internal/test_runner/test.js
+++ b/lib/internal/test_runner/test.js
@@ -278,6 +278,12 @@ class Test extends AsyncResource {
     };
     this.waitingOn = 0;
     this.finished = false;
+
+    if (!testOnlyFlag && (only || this.runOnlySubtests)) {
+      const warning =
+        "'only' and 'runOnly' require the --test-only command-line option.";
+      this.diagnostic(warning);
+    }
   }
 
   hasConcurrency() {
diff --git a/test/message/test_runner_output.out b/test/message/test_runner_output.out
index 15d2009816a961..1a165c33264e32 100644
--- a/test/message/test_runner_output.out
+++ b/test/message/test_runner_output.out
@@ -475,11 +475,13 @@ ok 52 - callback async throw after done
       ---
       duration_ms: *
       ...
+    # 'only' and 'runOnly' require the --test-only command-line option.
     # Subtest: running subtest 3
     ok 3 - running subtest 3
       ---
       duration_ms: *
       ...
+    # 'only' and 'runOnly' require the --test-only command-line option.
     # Subtest: running subtest 4
     ok 4 - running subtest 4
       ---
@@ -490,6 +492,7 @@ ok 53 - only is set but not in only mode
   ---
   duration_ms: *
   ...
+# 'only' and 'runOnly' require the --test-only command-line option.
 # Subtest: custom inspect symbol fail
 not ok 54 - custom inspect symbol fail
   ---
diff --git a/test/message/test_runner_output_cli.out b/test/message/test_runner_output_cli.out
index a76b37a77ce187..c351b1fa26fc83 100644
--- a/test/message/test_runner_output_cli.out
+++ b/test/message/test_runner_output_cli.out
@@ -475,11 +475,13 @@ ok 52 - callback async throw after done
       ---
       duration_ms: *
       ...
+    # 'only' and 'runOnly' require the --test-only command-line option.
     # Subtest: running subtest 3
     ok 3 - running subtest 3
       ---
       duration_ms: *
       ...
+    # 'only' and 'runOnly' require the --test-only command-line option.
     # Subtest: running subtest 4
     ok 4 - running subtest 4
       ---
@@ -490,6 +492,7 @@ ok 53 - only is set but not in only mode
   ---
   duration_ms: *
   ...
+# 'only' and 'runOnly' require the --test-only command-line option.
 # Subtest: custom inspect symbol fail
 not ok 54 - custom inspect symbol fail
   ---
diff --git a/test/message/test_runner_output_spec_reporter.out b/test/message/test_runner_output_spec_reporter.out
index 88ce796a783eeb..591dc9a76d64d0 100644
--- a/test/message/test_runner_output_spec_reporter.out
+++ b/test/message/test_runner_output_spec_reporter.out
@@ -199,9 +199,12 @@
  only is set but not in only mode
    running subtest 1 (*ms)
    running subtest 2 (*ms)
+   'only' and 'runOnly' require the --test-only command-line option.
    running subtest 3 (*ms)
+   'only' and 'runOnly' require the --test-only command-line option.
    running subtest 4 (*ms)
  only is set but not in only mode (*ms)
+ 'only' and 'runOnly' require the --test-only command-line option.
 
  custom inspect symbol fail (*ms)
   customized