diff --git a/src/server/utilitiesPublic.ts b/src/server/utilitiesPublic.ts
index 42f97a435f5..d234fe324ee 100644
--- a/src/server/utilitiesPublic.ts
+++ b/src/server/utilitiesPublic.ts
@@ -113,12 +113,12 @@ namespace ts.server {
         return /dev\/null\/inferredProject\d+\*/.test(name);
     }
 
-    export function makeInferredProjectName(counter: number) {
+    export function makeInferredProjectName(counter: number): string {
         return `/dev/null/inferredProject${counter}*`;
     }
 
     /*@internal*/
-    export function makeAutoImportProviderProjectName(counter: number) {
+    export function makeAutoImportProviderProjectName(counter: number): string {
         return `/dev/null/autoImportProviderProject${counter}*`;
     }