diff --git a/src/server/scriptInfo.ts b/src/server/scriptInfo.ts
index e362256b46b..0af6808d892 100644
--- a/src/server/scriptInfo.ts
+++ b/src/server/scriptInfo.ts
@@ -559,7 +559,7 @@ namespace ts.server {
             }
         }
 
-        getLatestVersion() {
+        getLatestVersion(): string {
             // Ensure we have updated snapshot to give back latest version
             this.textStorage.getSnapshot();
             return this.textStorage.getVersion();