diff --git a/src/harness/unittests/tsserverProjectSystem.ts b/src/harness/unittests/tsserverProjectSystem.ts
index 783a6016f7a..13d8a6bf824 100644
--- a/src/harness/unittests/tsserverProjectSystem.ts
+++ b/src/harness/unittests/tsserverProjectSystem.ts
@@ -1799,7 +1799,6 @@ namespace ts.projectSystem {
         });
 
         it("language service disabled state is updated in external projects", () => {
-            debugger
             const f1 = {
                 path: "/a/app.js",
                 content: "var x = 1"
@@ -1940,6 +1939,31 @@ namespace ts.projectSystem {
             const edits = project.getLanguageService().getFormattingEditsForDocument(f1.path, options);
             assert.deepEqual(edits, [{ span: createTextSpan(/*start*/ 7, /*length*/ 3), newText: " " }]);
         });
+
+        it("snapshot from different caches are incompatible", () => {
+            const f1 = {
+                path: "/a/b/app.ts",
+                content: "let x = 1;"
+            };
+            const host = createServerHost([f1]);
+            const projectFileName = "/a/b/proj.csproj";
+            const projectService = createProjectService(host);
+            projectService.openExternalProject({
+                projectFileName,
+                rootFiles: [toExternalFile(f1.path)],
+                options: {}
+            })
+            projectService.openClientFile(f1.path, "let x = 1;\nlet y = 2;");
+
+            projectService.checkNumberOfProjects({ externalProjects: 1 });
+            projectService.externalProjects[0].getLanguageService(/*ensureSynchronized*/false).getNavigationBarItems(f1.path);
+            projectService.closeClientFile(f1.path);
+
+            projectService.openClientFile(f1.path);
+            projectService.checkNumberOfProjects({ externalProjects: 1 });
+            const navbar = projectService.externalProjects[0].getLanguageService(/*ensureSynchronized*/false).getNavigationBarItems(f1.path);
+            assert.equal(navbar[0].spans[0].length, f1.content.length);
+        });
     });
 
     describe("Proper errors", () => {
diff --git a/src/server/scriptVersionCache.ts b/src/server/scriptVersionCache.ts
index aaf04d39a1f..e087c3b6dde 100644
--- a/src/server/scriptVersionCache.ts
+++ b/src/server/scriptVersionCache.ts
@@ -398,7 +398,7 @@ namespace ts.server {
         index: LineIndex;
         changesSincePreviousVersion: TextChange[] = [];
 
-        constructor(public version: number, public cache: ScriptVersionCache) {
+        constructor(readonly version: number, readonly cache: ScriptVersionCache) {
         }
 
         getText(rangeStart: number, rangeEnd: number) {
@@ -438,7 +438,7 @@ namespace ts.server {
             }
         }
         getChangeRange(oldSnapshot: ts.IScriptSnapshot): ts.TextChangeRange {
-            if (oldSnapshot instanceof LineIndexSnapshot) {
+            if (oldSnapshot instanceof LineIndexSnapshot && this.cache === oldSnapshot.cache) {
                 return this.getTextChangeRangeSinceVersion(oldSnapshot.version);
             }
         }