diff --git a/packages/jupyterlab-lsp/src/features/completion.ts b/packages/jupyterlab-lsp/src/features/completion.ts
index ea4068d01..a770508cd 100644
--- a/packages/jupyterlab-lsp/src/features/completion.ts
+++ b/packages/jupyterlab-lsp/src/features/completion.ts
@@ -94,7 +94,10 @@ export class CompletionLabIntegration implements IFeatureLabIntegration {
   ) {
     if (this.current_adapter) {
       // disconnect signals from the old adapter
-      this.current_adapter.activeEditorChanged.disconnect(this.set_connector, this);
+      this.current_adapter.activeEditorChanged.disconnect(
+        this.set_connector,
+        this
+      );
       this.current_adapter.adapterConnected.disconnect(
         this.connect_completion,
         this
@@ -107,7 +110,7 @@ export class CompletionLabIntegration implements IFeatureLabIntegration {
       this.connect_completion,
       this
     );
-    this.set_connector(adapter, {editor: adapter.activeEditor});
+    this.set_connector(adapter, { editor: adapter.activeEditor });
   }
 
   connect_completion(
diff --git a/packages/jupyterlab-lsp/src/features/diagnostics.ts b/packages/jupyterlab-lsp/src/features/diagnostics.ts
index 12795770b..2840c9b3d 100644
--- a/packages/jupyterlab-lsp/src/features/diagnostics.ts
+++ b/packages/jupyterlab-lsp/src/features/diagnostics.ts
@@ -288,12 +288,25 @@ export class DiagnosticsCM extends CodeMirrorIntegration {
           const end = PositionConverter.lsp_to_cm(
             range.end
           ) as IVirtualPosition;
-          if (start.line > this.virtual_document.last_virtual_line) {
+          const last_line_number = this.virtual_document.last_virtual_line;
+          if (start.line > last_line_number) {
             console.log(
-              'Malformed diagnostic was skipped (out of lines) ',
+              `Out of range diagnostic (${start.line} line > ${last_line_number}) was skipped `,
               diagnostics
             );
             return;
+          } else {
+            let last_line = this.virtual_document.last_line;
+            if (
+              start.line == this.virtual_document.last_virtual_line &&
+              start.ch > last_line.length
+            ) {
+              console.log(
+                `Out of range diagnostic (${start.ch} character > ${last_line.length} at line ${last_line_number}) was skipped `,
+                diagnostics
+              );
+              return;
+            }
           }
 
           let document: VirtualDocument;
diff --git a/packages/jupyterlab-lsp/src/virtual/codemirror_editor.ts b/packages/jupyterlab-lsp/src/virtual/codemirror_editor.ts
index a3da0959f..f84fe83d6 100644
--- a/packages/jupyterlab-lsp/src/virtual/codemirror_editor.ts
+++ b/packages/jupyterlab-lsp/src/virtual/codemirror_editor.ts
@@ -2,7 +2,12 @@ import * as CodeMirror from 'codemirror';
 import { CodeMirrorEditor } from '@jupyterlab/codemirror';
 import { CodeEditor } from '@jupyterlab/codeeditor';
 import { IEditorName } from '../feature';
-import { IBlockAddedInfo, ICodeBlockOptions, UpdateManager, VirtualDocument } from './document';
+import {
+  IBlockAddedInfo,
+  ICodeBlockOptions,
+  UpdateManager,
+  VirtualDocument
+} from './document';
 import { IForeignCodeExtractorsRegistry } from '../extractors/types';
 import { create_console, EditorLogConsole } from './console';
 import { Signal } from '@lumino/signaling';
@@ -115,7 +120,10 @@ export class CodeMirrorVirtualEditor
       }
     });
     // this is not thee most efficient, but probably the most reliable way
-    this.virtual_document.update_manager.update_began.connect(this.onEditorsUpdated, this);
+    this.virtual_document.update_manager.update_began.connect(
+      this.onEditorsUpdated,
+      this
+    );
 
     this.virtual_document.update_manager.block_added.connect(
       this.save_block_position,
@@ -165,7 +173,10 @@ export class CodeMirrorVirtualEditor
     return this.getDoc().getCursor('end') as IRootPosition;
   }
 
-  private onEditorsUpdated(update_manager: UpdateManager, blocks: ICodeBlockOptions[]): void {
+  private onEditorsUpdated(
+    update_manager: UpdateManager,
+    blocks: ICodeBlockOptions[]
+  ): void {
     this.cm_editor_to_ce_editor.clear();
     this.ce_editor_to_cm_editor.clear();
     this.editor_to_source_line_new = new Map();
diff --git a/packages/jupyterlab-lsp/src/virtual/document.ts b/packages/jupyterlab-lsp/src/virtual/document.ts
index cddfc601a..2549ae25c 100644
--- a/packages/jupyterlab-lsp/src/virtual/document.ts
+++ b/packages/jupyterlab-lsp/src/virtual/document.ts
@@ -642,6 +642,10 @@ export class VirtualDocument {
     return this.lines.join(lines_padding);
   }
 
+  get last_line() {
+    return this.lines[this.lines.length];
+  }
+
   close_expired_documents() {
     for (let document of this.unused_documents.values()) {
       document.remaining_lifetime -= 1;
@@ -816,8 +820,9 @@ export class UpdateManager {
    */
   private document_updated: Signal<UpdateManager, VirtualDocument>;
   public block_added: Signal<UpdateManager, IBlockAddedInfo>;
-  // possibly redundant
-  update_done: Promise<void> = new Promise<void>(() => {});
+  update_done: Promise<void> = new Promise<void>(resolve => {
+    resolve();
+  });
   update_began: Signal<UpdateManager, ICodeBlockOptions[]>;
   update_finished: Signal<UpdateManager, ICodeBlockOptions[]>;