diff --git a/src/server/protocol.ts b/src/server/protocol.ts
index acffd6bde5c..e956290181a 100644
--- a/src/server/protocol.ts
+++ b/src/server/protocol.ts
@@ -2521,6 +2521,7 @@ namespace ts.server.protocol {
         maxFileSize: number;
     }
 
+    /*@internal*/
     export type AnyEvent = RequestCompletedEvent | DiagnosticEvent | ConfigFileDiagnosticEvent | ProjectLanguageServiceStateEvent | TelemetryEvent |
         ProjectsUpdatedInBackgroundEvent | ProjectLoadingStartEvent | ProjectLoadingFinishEvent | SurveyReadyEvent | LargeFileReferencedEvent;
 
diff --git a/tests/baselines/reference/api/tsserverlibrary.d.ts b/tests/baselines/reference/api/tsserverlibrary.d.ts
index ccc9557e948..b5ef0cac750 100644
--- a/tests/baselines/reference/api/tsserverlibrary.d.ts
+++ b/tests/baselines/reference/api/tsserverlibrary.d.ts
@@ -7486,6 +7486,7 @@ declare namespace ts.server.protocol {
      */
     interface DiagnosticEvent extends Event {
         body?: DiagnosticEventBody;
+        event: DiagnosticEventKind;
     }
     interface ConfigFileDiagnosticEventBody {
         /**