diff --git a/src/server/project.ts b/src/server/project.ts
index d4944d8d9c5..669928d70b4 100644
--- a/src/server/project.ts
+++ b/src/server/project.ts
@@ -392,8 +392,8 @@ export abstract class Project implements LanguageServiceHost, ModuleResolutionHo
 
     public languageServiceEnabled: boolean;
 
-    trace?(s: string): void;
-    realpath?(path: string): string;
+    readonly trace?: (s: string) => void;
+    readonly realpath?: (path: string) => string;
 
     /** @internal */
     hasInvalidatedResolutions?: HasInvalidatedResolutions | undefined;