diff --git a/src/popover/popover.directive.ts b/src/popover/popover.directive.ts
index dd006395af..ba7ba4a5b5 100644
--- a/src/popover/popover.directive.ts
+++ b/src/popover/popover.directive.ts
@@ -37,7 +37,7 @@ export class PopoverDirective implements OnInit, OnDestroy {
   /**
    * Css class for popover container
    */
-  @Input() public containerClass: string;
+  @Input() public containerClass: string = '';
 
   /**
    * Returns whether or not the popover is currently being shown