diff --git a/src/server/project.ts b/src/server/project.ts
index 4adbc7ca059..267175f5699 100644
--- a/src/server/project.ts
+++ b/src/server/project.ts
@@ -414,6 +414,9 @@ namespace ts.server {
                         removed.push(id);
                     }
                 }
+                if (added.length > 0 || removed.length > 0) {
+                    this.projectService.typingsCache.invalidateCachedTypingsForProject(this);
+                }
                 this.lastReportedFileNames = currentFiles;
 
                 this.lastReportedFileNames = currentFiles;