diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index 3412c1c1598f7..47ab9e6a12f62 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -2414,7 +2414,7 @@ namespace ts.server {
                     this.openFilesWithNonRootedDiskPath.set(this.toCanonicalFileName(fileName), info);
                 }
             }
-            if (openedByClient && !info.isScriptOpen()) {
+            if (openedByClient) {
                 // Opening closed script info
                 // either it was created just now, or was part of projects but was closed
                 this.stopWatchingScriptInfo(info);
@@ -2423,9 +2423,6 @@ namespace ts.server {
                     info.registerFileUpdate();
                 }
             }
-            else {
-                Debug.assert(fileContent === undefined);
-            }
             return info;
         }
 
@@ -3170,11 +3167,9 @@ namespace ts.server {
                     const iterResult = openFiles.next();
                     if (iterResult.done) break;
                     const file = iterResult.value;
-                    const scriptInfo = this.getScriptInfo(file.fileName);
-                    Debug.assert(!scriptInfo || !scriptInfo.isScriptOpen(), "Script should not exist and not be open already");
                     // Create script infos so we have the new content for all the open files before we do any updates to projects
                     const info = this.getOrCreateOpenScriptInfo(
-                        scriptInfo ? scriptInfo.fileName : toNormalizedPath(file.fileName),
+                        toNormalizedPath(file.fileName),
                         file.content,
                         tryConvertScriptKindName(file.scriptKind!),
                         file.hasMixedContent,
diff --git a/src/testRunner/unittests/tsserver/applyChangesToOpenFiles.ts b/src/testRunner/unittests/tsserver/applyChangesToOpenFiles.ts
index 316ecc8b65234..6d5ee91d68d67 100644
--- a/src/testRunner/unittests/tsserver/applyChangesToOpenFiles.ts
+++ b/src/testRunner/unittests/tsserver/applyChangesToOpenFiles.ts
@@ -29,7 +29,11 @@ ${file.content}`;
             assert.equal(Number(project.getProjectVersion()), expected);
         }
 
-        function verify(applyChangesToOpen: (session: TestSession) => void) {
+        interface Verify {
+            applyChangesToOpen: (session: TestSession) => void;
+            openFile1Again: (session: TestSession) => void;
+        }
+        function verify({ applyChangesToOpen, openFile1Again }: Verify) {
             const host = createServerHost([app, file3, commonFile1, commonFile2, libFile, configFile]);
             const session = createSession(host);
             session.executeCommandSeq<protocol.OpenRequest>({
@@ -65,11 +69,22 @@ ${file.content}`;
             verifyText(service, commonFile2.path, fileContentWithComment(commonFile2));
             verifyText(service, app.path, "let zzz = 10;let zz = 10;let z = 1;");
             verifyText(service, file3.path, file3.content);
+
+            // Open file1 again
+            openFile1Again(session);
+            assert.isTrue(service.getScriptInfo(commonFile1.path)!.isScriptOpen());
+
+            // Verify that file1 contents are changed
+            verifyProjectVersion(project, 4);
+            verifyText(service, commonFile1.path, commonFile1.content);
+            verifyText(service, commonFile2.path, fileContentWithComment(commonFile2));
+            verifyText(service, app.path, "let zzz = 10;let zz = 10;let z = 1;");
+            verifyText(service, file3.path, file3.content);
         }
 
         it("with applyChangedToOpenFiles request", () => {
-            verify(session =>
-                session.executeCommandSeq<protocol.ApplyChangedToOpenFilesRequest>({
+            verify({
+                applyChangesToOpen: session => session.executeCommandSeq<protocol.ApplyChangedToOpenFilesRequest>({
                     command: protocol.CommandTypes.ApplyChangedToOpenFiles,
                     arguments: {
                         openFiles: [
@@ -101,13 +116,22 @@ ${file.content}`;
                             file3.path
                         ]
                     }
-                })
-            );
+                }),
+                openFile1Again: session => session.executeCommandSeq<protocol.ApplyChangedToOpenFilesRequest>({
+                    command: protocol.CommandTypes.ApplyChangedToOpenFiles,
+                    arguments: {
+                        openFiles: [{
+                            fileName: commonFile1.path,
+                            content: commonFile1.content
+                        }]
+                    }
+                }),
+            });
         });
 
         it("with updateOpen request", () => {
-            verify(session =>
-                session.executeCommandSeq<protocol.UpdateOpenRequest>({
+            verify({
+                applyChangesToOpen: session => session.executeCommandSeq<protocol.UpdateOpenRequest>({
                     command: protocol.CommandTypes.UpdateOpen,
                     arguments: {
                         openFiles: [
@@ -141,8 +165,17 @@ ${file.content}`;
                             file3.path
                         ]
                     }
-                })
-            );
+                }),
+                openFile1Again: session => session.executeCommandSeq<protocol.UpdateOpenRequest>({
+                    command: protocol.CommandTypes.UpdateOpen,
+                    arguments: {
+                        openFiles: [{
+                            file: commonFile1.path,
+                            fileContent: commonFile1.content
+                        }]
+                    }
+                }),
+            });
         });
     });
 }
diff --git a/src/testRunner/unittests/tsserver/openFile.ts b/src/testRunner/unittests/tsserver/openFile.ts
index d2a995c68f88e..62a7fcc729ac8 100644
--- a/src/testRunner/unittests/tsserver/openFile.ts
+++ b/src/testRunner/unittests/tsserver/openFile.ts
@@ -104,5 +104,29 @@ namespace ts.projectSystem {
                 checkProjectActualFiles(project, files.map(f => f.path));
             }
         });
+
+        it("can open same file again", () => {
+            const projectFolder = "/user/someuser/projects/myproject";
+            const aFile: File = {
+                path: `${projectFolder}/src/a.ts`,
+                content: "export const x = 0;"
+            };
+            const configFile: File = {
+                path: `${projectFolder}/tsconfig.json`,
+                content: "{}"
+            };
+            const files = [aFile, configFile, libFile];
+            const host = createServerHost(files);
+            const service = createProjectService(host);
+            verifyProject(aFile.content);
+            verifyProject(`${aFile.content}export const y = 10;`);
+
+            function verifyProject(aFileContent: string) {
+                service.openClientFile(aFile.path, aFileContent, ScriptKind.TS, projectFolder);
+                const project = service.configuredProjects.get(configFile.path)!;
+                checkProjectActualFiles(project, files.map(f => f.path));
+                assert.equal(project.getCurrentProgram()?.getSourceFile(aFile.path)!.text, aFileContent);
+            }
+        });
     });
 }