diff --git a/platform/ios/src/MGLMapboxEvents.m b/platform/ios/src/MGLMapboxEvents.m
index 0967257bf..681b95b87 100644
--- a/platform/ios/src/MGLMapboxEvents.m
+++ b/platform/ios/src/MGLMapboxEvents.m
@@ -240,6 +240,7 @@ const NSTimeInterval MGLFlushInterval = 180;
 }
 
 - (void)userDefaultsDidChange:(NSNotification *)notification {
+    MGLAssertIsMainThread();
     [self pauseOrResumeMetricsCollectionIfRequired];
 }