diff --git a/STPopup/UIViewController+STPopup.m b/STPopup/UIViewController+STPopup.m
index b80a977..408e26a 100644
--- a/STPopup/UIViewController+STPopup.m
+++ b/STPopup/UIViewController+STPopup.m
@@ -64,7 +64,9 @@ - (void)st_viewDidLoad
 - (void)st_presentViewController:(UIViewController *)viewControllerToPresent animated:(BOOL)flag completion:(void (^)(void))completion
 {
     if (!self.popupController) {
-        [self st_presentViewController:viewControllerToPresent animated:flag completion:completion];
+        if (viewControllerToPresent != nil) {
+            [self st_presentViewController:viewControllerToPresent animated:flag completion:completion];
+        }
         return;
     }
     
@@ -157,4 +159,4 @@ - (STPopupController *)popupController
     return popupController;
 }
 
-@end
\ No newline at end of file
+@end