diff --git a/platform/ios/app/MBXViewController.m b/platform/ios/app/MBXViewController.m
index 5176692e1d9..ef91c847be2 100644
--- a/platform/ios/app/MBXViewController.m
+++ b/platform/ios/app/MBXViewController.m
@@ -639,6 +639,8 @@ - (MGLAnnotationImage *)mapView:(MGLMapView * __nonnull)mapView imageForAnnotati
         return nil; // use default marker
     }
 
+    NSAssert([annotation isKindOfClass:[MBXSpriteBackedAnnotation class]], @"Annotations should be sprite-backed.");
+
     NSString *title = [(MGLPointAnnotation *)annotation title];
     if (!title.length) return nil;
     NSString *lastTwoCharacters = [title substringFromIndex:title.length - 2];