diff --git a/src/tooltip/tooltip.spec.ts b/src/tooltip/tooltip.spec.ts
index b0288608e3..6b6a4f97b6 100644
--- a/src/tooltip/tooltip.spec.ts
+++ b/src/tooltip/tooltip.spec.ts
@@ -3,12 +3,13 @@ import {createGenericTestComponent, createKeyEvent, triggerEvent} from '../test/
 
 import {By} from '@angular/platform-browser';
 import {
-  Component,
-  ViewChild,
+  AfterViewInit,
   ChangeDetectionStrategy,
+  ChangeDetectorRef,
+  Component,
   TemplateRef,
-  ViewContainerRef,
-  AfterViewInit
+  ViewChild,
+  ViewContainerRef
 } from '@angular/core';
 
 import {Key} from '../util/key';
@@ -59,7 +60,6 @@ describe('ngb-tooltip-window', () => {
 
     expect(fixture.nativeElement).toHaveCssClass('my-custom-class');
   });
-
 });
 
 describe('ngb-tooltip', () => {
diff --git a/src/tooltip/tooltip.ts b/src/tooltip/tooltip.ts
index 093d6af663..154fba2b23 100644
--- a/src/tooltip/tooltip.ts
+++ b/src/tooltip/tooltip.ts
@@ -18,7 +18,9 @@ import {
   NgZone,
   ViewEncapsulation,
   ChangeDetectorRef,
-  ApplicationRef
+  ApplicationRef,
+  OnChanges,
+  SimpleChanges
 } from '@angular/core';
 import {DOCUMENT} from '@angular/common';
 
@@ -48,7 +50,7 @@ export class NgbTooltipWindow {
  * A lightweight and extensible directive for fancy tooltip creation.
  */
 @Directive({selector: '[ngbTooltip]', exportAs: 'ngbTooltip'})
-export class NgbTooltip implements OnInit, OnDestroy {
+export class NgbTooltip implements OnInit, OnDestroy, OnChanges {
   /**
    * Indicates whether the tooltip should be closed on `Escape` key and inside/outside clicks:
    *
@@ -253,6 +255,12 @@ export class NgbTooltip implements OnInit, OnDestroy {
         this.close.bind(this), +this.openDelay, +this.closeDelay);
   }
 
+  ngOnChanges({tooltipClass}: SimpleChanges) {
+    if (tooltipClass && this.isOpen()) {
+      this._windowRef.instance.tooltipClass = tooltipClass.currentValue;
+    }
+  }
+
   ngOnDestroy() {
     this.close();
     // This check is needed as it might happen that ngOnDestroy is called before ngOnInit