diff --git a/src/harness/unittests/tsserverProjectSystem.ts b/src/harness/unittests/tsserverProjectSystem.ts
index 3e68688de8885..e960a8cbb888a 100644
--- a/src/harness/unittests/tsserverProjectSystem.ts
+++ b/src/harness/unittests/tsserverProjectSystem.ts
@@ -3181,7 +3181,7 @@ namespace ts.projectSystem {
             const projectLocation = "/user/username/projects/project";
             const file1: FileOrFolder = {
                 path: `${projectLocation}/src/file1.ts`,
-                content: `import { y } from "./file1"; let x = 10;`
+                content: `import { y } from "./file2"; let x = 10;`
             };
             const file2: FileOrFolder = {
                 path: `${projectLocation}/src/file2.ts`,
@@ -3259,6 +3259,53 @@ namespace ts.projectSystem {
             // Allow allowNonTsExtensions will be set to true for deferred extensions.
             assert.isTrue(configuredProject.getCompilerOptions().allowNonTsExtensions);
         });
+
+        it("Orphan source files are handled correctly on watch trigger", () => {
+            const projectLocation = "/user/username/projects/project";
+            const file1: FileOrFolder = {
+                path: `${projectLocation}/src/file1.ts`,
+                content: `export let x = 10;`
+            };
+            const file2: FileOrFolder = {
+                path: `${projectLocation}/src/file2.ts`,
+                content: "export let y = 10;"
+            };
+            const configContent1 = JSON.stringify({
+                files: ["src/file1.ts", "src/file2.ts"]
+            });
+            const config: FileOrFolder = {
+                path: `${projectLocation}/tsconfig.json`,
+                content: configContent1
+            };
+            const files = [file1, file2, libFile, config];
+            const host = createServerHost(files);
+            const service = createProjectService(host);
+            service.openClientFile(file1.path);
+            checkProjectActualFiles(service.configuredProjects.get(config.path), [file1.path, file2.path, libFile.path, config.path]);
+
+            const configContent2 = JSON.stringify({
+                files: ["src/file1.ts"]
+            });
+            config.content = configContent2;
+            host.reloadFS(files);
+            host.runQueuedTimeoutCallbacks();
+
+            checkProjectActualFiles(service.configuredProjects.get(config.path), [file1.path, libFile.path, config.path]);
+            verifyFile2InfoIsOrphan();
+
+            file2.content += "export let z = 10;";
+            host.reloadFS(files);
+            host.runQueuedTimeoutCallbacks();
+
+            checkProjectActualFiles(service.configuredProjects.get(config.path), [file1.path, libFile.path, config.path]);
+            verifyFile2InfoIsOrphan();
+
+            function verifyFile2InfoIsOrphan() {
+                const info = service.getScriptInfoForPath(file2.path as Path);
+                assert.isDefined(info);
+                assert.equal(info.containingProjects.length, 0);
+            }
+        });
     });
 
     describe("tsserverProjectSystem Proper errors", () => {
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index b835e566372c6..d66fe48682e63 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -594,10 +594,12 @@ namespace ts.server {
         }
 
         private delayUpdateProjectGraphs(projects: ReadonlyArray<Project>) {
-            for (const project of projects) {
-                this.delayUpdateProjectGraph(project);
+            if (projects.length) {
+                for (const project of projects) {
+                    this.delayUpdateProjectGraph(project);
+                }
+                this.delayEnsureProjectForOpenFiles();
             }
-            this.delayEnsureProjectForOpenFiles();
         }
 
         setCompilerOptionsForInferredProjects(projectCompilerOptions: protocol.ExternalProjectCompilerOptions, projectRootPath?: string): void {
@@ -708,7 +710,6 @@ namespace ts.server {
                 this.handleDeletedFile(info);
             }
             else if (!info.isScriptOpen()) {
-                Debug.assert(info.containingProjects.length !== 0);
                 // file has been changed which might affect the set of referenced files in projects that include
                 // this file and set of inferred projects
                 info.delayReloadNonMixedContentFile();