diff --git a/org.eclipse.xtext.ui.tests/src-longrunning/org/eclipse/xtext/ui/tests/editor/DirtyStateEditorSupportIntegrationTest.java b/org.eclipse.xtext.ui.tests/src-longrunning/org/eclipse/xtext/ui/tests/editor/DirtyStateEditorSupportIntegrationTest.java
index 7aff6f28075..063b9e31276 100644
--- a/org.eclipse.xtext.ui.tests/src-longrunning/org/eclipse/xtext/ui/tests/editor/DirtyStateEditorSupportIntegrationTest.java
+++ b/org.eclipse.xtext.ui.tests/src-longrunning/org/eclipse/xtext/ui/tests/editor/DirtyStateEditorSupportIntegrationTest.java
@@ -8,28 +8,36 @@
  */
 package org.eclipse.xtext.ui.tests.editor;
 
+import java.io.File;
+import java.io.FileWriter;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
 
 import org.eclipse.core.resources.IFile;
+import org.eclipse.core.resources.ResourcesPlugin;
 import org.eclipse.core.runtime.NullProgressMonitor;
+import org.eclipse.core.runtime.jobs.Job;
 import org.eclipse.emf.common.util.URI;
 import org.eclipse.jface.text.IUndoManager;
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.custom.StyledText;
 import org.eclipse.swt.widgets.Display;
 import org.eclipse.swt.widgets.Event;
+import org.eclipse.ui.IFileEditorInput;
+import org.eclipse.ui.editors.text.FileDocumentProvider;
 import org.eclipse.xtext.resource.IEObjectDescription;
 import org.eclipse.xtext.resource.IResourceDescription;
 import org.eclipse.xtext.resource.IResourceServiceProvider;
 import org.eclipse.xtext.ui.editor.XtextEditor;
 import org.eclipse.xtext.ui.editor.XtextSourceViewer;
+import org.eclipse.xtext.ui.editor.model.IXtextDocument;
 import org.eclipse.xtext.ui.refactoring.ui.SyncUtil;
 import org.eclipse.xtext.ui.testing.AbstractEditorTest;
 import org.eclipse.xtext.ui.testing.util.IResourcesSetupUtil;
 import org.junit.Assert;
 import org.junit.Before;
+import org.junit.Ignore;
 import org.junit.Test;
 
 import com.google.common.collect.Iterables;
@@ -116,7 +124,68 @@ public void testUndoRedo() throws Exception {
 				.getQualifiedName().getLastSegment());
 		Iterables.getLast(events);
 	}
+	
+	/*
+	 * @see https://github.com/eclipse/xtext/issues/2385
+	 */
+	@Test public void testModifyFileInExternEditor() throws Exception {
+		IXtextDocument document = editor.getDocument();
+
+		Display.getDefault().readAndDispatch();
+		
+		assertNotEquals(document.get(), "");
+		assertTrue(editor.getDocumentProvider() instanceof FileDocumentProvider);
+		
+		FileDocumentProvider fileDocumentProvider = (FileDocumentProvider)editor.getDocumentProvider();
+		
+		getWorkbench().getActiveWorkbenchWindow().getActivePage().getViewReferences()[0].getView(false).setFocus();
+		
+		File externalEditFile = ((IFileEditorInput)editor.getEditorInput()).getFile().getLocation().toFile();
+		try (FileWriter fw = new FileWriter(externalEditFile)) {
+			fw.write("");
+		}
+		editor.setFocus();
+		Job.getJobManager().join(ResourcesPlugin.FAMILY_AUTO_REFRESH, null);
+		syncUtil.yieldToQueuedDisplayJobs(new NullProgressMonitor());
+		syncUtil.waitForReconciler(editor);
+		
+		assertTrue(fileDocumentProvider.isSynchronized(editor.getEditorInput()));
+		
+		assertEquals(document.get(), "");
+	}
+
+	/**
+	 * This test needs a manual button click.
+	 */
+	@Ignore
+	@Test public void testModifyDirtyFileInExternEditor() throws Exception {
+		IXtextDocument document = editor.getDocument();
 
+		Display.getDefault().readAndDispatch();
+		
+		assertNotEquals(document.get(), "");
+		document.set("/* Hello World! */");
+		assertEquals("/* Hello World! */", document.get());
+		assertTrue(editor.isDirty());
+		
+		getWorkbench().getActiveWorkbenchWindow().getActivePage().getViewReferences()[0].getView(false).setFocus();
+		
+		File externalEditFile = ((IFileEditorInput)editor.getEditorInput()).getFile().getLocation().toFile();
+		try (FileWriter fw = new FileWriter(externalEditFile)) {
+			fw.write("");
+		}
+		editor.setFocus();
+		// Dialog opens and the "Ignore file change" button has to be clicked.
+		Job.getJobManager().join(ResourcesPlugin.FAMILY_AUTO_REFRESH, null);
+		syncUtil.yieldToQueuedDisplayJobs(new NullProgressMonitor());
+		syncUtil.waitForReconciler(editor);
+		assertEquals(document.get(), "/* Hello World! */");
+		
+		assertTrue(editor.isDirty());
+		editor.doSave(new NullProgressMonitor());
+		assertFalse(editor.isDirty());
+	}
+	
 	private IEObjectDescription getFirstExportedObjectInLastEventDelta() {
 		return Iterables.getFirst(Iterables.getLast(events).getDeltas().get(0).getNew().getExportedObjects(), null);
 	}
diff --git a/org.eclipse.xtext.ui/src/org/eclipse/xtext/ui/editor/XtextEditor.java b/org.eclipse.xtext.ui/src/org/eclipse/xtext/ui/editor/XtextEditor.java
index 11159105a22..c1fd4b599e8 100755
--- a/org.eclipse.xtext.ui/src/org/eclipse/xtext/ui/editor/XtextEditor.java
+++ b/org.eclipse.xtext.ui/src/org/eclipse/xtext/ui/editor/XtextEditor.java
@@ -76,6 +76,8 @@
 import org.eclipse.ui.PlatformUI;
 import org.eclipse.ui.editors.text.TextEditor;
 import org.eclipse.ui.texteditor.DefaultMarkerAnnotationAccess;
+import org.eclipse.ui.texteditor.IDocumentProvider;
+import org.eclipse.ui.texteditor.IDocumentProviderExtension3;
 import org.eclipse.ui.texteditor.ITextEditor;
 import org.eclipse.ui.texteditor.ITextEditorActionConstants;
 import org.eclipse.ui.texteditor.ITextEditorActionDefinitionIds;
@@ -327,6 +329,20 @@ public void doSave(IProgressMonitor progressMonitor) {
 		callback.afterSave(this);
 	}
 	
+	@Override
+	protected void performSave(boolean overwrite, IProgressMonitor progressMonitor) {
+		super.performSave(overwrite || isSynchronized(), progressMonitor);
+	}
+	
+	
+	private boolean isSynchronized() {
+		IResource resource = getResource();
+		if (resource != null) {
+			return resource.isSynchronized(IResource.DEPTH_ZERO);
+		}
+		return false;
+	}
+
 	@Override
 	protected void updateState(final IEditorInput input) {
 		new DisplayRunnable() {
diff --git a/org.eclipse.xtext.ui/src/org/eclipse/xtext/ui/editor/model/XtextDocumentProvider.java b/org.eclipse.xtext.ui/src/org/eclipse/xtext/ui/editor/model/XtextDocumentProvider.java
index c8a804bf3ca..9fc94d3e1fc 100644
--- a/org.eclipse.xtext.ui/src/org/eclipse/xtext/ui/editor/model/XtextDocumentProvider.java
+++ b/org.eclipse.xtext.ui/src/org/eclipse/xtext/ui/editor/model/XtextDocumentProvider.java
@@ -408,20 +408,6 @@ public long getModificationStamp(Object element) {
 		}
 	}
 	
-	@Override
-	public boolean isSynchronized(Object element) {
-		ElementInfo info = getElementInfo(element);
-		long synchronizationStamp;
-		if (info instanceof FileInfo) {
-			synchronizationStamp = ((FileInfo) info).fModificationStamp;
-		} else if (info instanceof URIInfo) {
-			synchronizationStamp = ((URIInfo) info).synchronizationStamp;
-		} else {
-			return super.isSynchronized(element);
-		}
-		return synchronizationStamp == getModificationStamp(element);
-	}
-	
 	@Override
 	public boolean isModifiable(Object element) {
 		if (isWorkspaceExternalEditorInput(element)) {