diff --git a/lib/internal/test_runner/test.js b/lib/internal/test_runner/test.js
index 48271e2e71a80e..95522faa6a73d2 100644
--- a/lib/internal/test_runner/test.js
+++ b/lib/internal/test_runner/test.js
@@ -288,6 +288,12 @@ 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 cc9c07f4c5c409..9ee9073844700d 100644
--- a/test/message/test_runner_output_cli.out
+++ b/test/message/test_runner_output_cli.out
@@ -476,11 +476,13 @@ TAP version 13
           ---
           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
           ---
@@ -491,6 +493,7 @@ TAP version 13
       ---
       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 cf47c7ac7e33ff..cff846c3959cca 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