diff --git a/CHANGELOG.md b/CHANGELOG.md
index cf184ea1d..40c3622fa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,7 +5,8 @@
 ### Fixes
 
 * Maps with Key Object, Object would fail during serialization if not String, Object ([#935](https://github.com/getsentry/sentry-dart/pull/935))
-* Fix duplicative Screen size changed breadcrumbs ([#888](https://github.com/getsentry/sentry-dart/pull/888))
+* Breadcrumbs "Concurrent Modification" ([#948](https://github.com/getsentry/sentry-dart/pull/948))
+* Duplicative Screen size changed breadcrumbs ([#888](https://github.com/getsentry/sentry-dart/pull/888))
 
 ### Features
 
diff --git a/dart/lib/src/scope.dart b/dart/lib/src/scope.dart
index e0a4fe090..0802975af 100644
--- a/dart/lib/src/scope.dart
+++ b/dart/lib/src/scope.dart
@@ -390,29 +390,29 @@ class Scope {
 
     await clone.setUser(user);
 
-    for (final tag in _tags.keys) {
+    for (final tag in List.from(_tags.keys)) {
       await clone.setTag(tag, _tags[tag]!);
     }
 
-    for (final extraKey in _extra.keys) {
+    for (final extraKey in List.from(_extra.keys)) {
       await clone.setExtra(extraKey, _extra[extraKey]);
     }
 
-    for (final breadcrumb in _breadcrumbs) {
+    for (final breadcrumb in List.from(_breadcrumbs)) {
       await clone.addBreadcrumb(breadcrumb);
     }
 
-    for (final eventProcessor in _eventProcessors) {
+    for (final eventProcessor in List.from(_eventProcessors)) {
       clone.addEventProcessor(eventProcessor);
     }
 
-    contexts.forEach((key, value) {
-      if (value != null) {
-        clone.setContexts(key, value);
+    for (final entry in Map.from(contexts).entries) {
+      if (entry.value != null) {
+        await clone.setContexts(entry.key, entry.value);
       }
-    });
+    }
 
-    for (final attachment in _attachments) {
+    for (final attachment in List.from(_attachments)) {
       clone.addAttachment(attachment);
     }
 
diff --git a/dart/test/sentry_client_test.dart b/dart/test/sentry_client_test.dart
index 8bd7c06b4..f0c1085f8 100644
--- a/dart/test/sentry_client_test.dart
+++ b/dart/test/sentry_client_test.dart
@@ -553,12 +553,12 @@ void main() {
       breadcrumbs: eventCrumbs,
     );
 
-    Scope createScope(SentryOptions options) {
+    Future<Scope> createScope(SentryOptions options) async {
       final scope = Scope(options)
         ..transaction = transaction
-        ..fingerprint = fingerprint
-        ..addBreadcrumb(crumb);
-      scope.setUser(user);
+        ..fingerprint = fingerprint;
+      await scope.addBreadcrumb(crumb);
+      await scope.setUser(user);
       return scope;
     }
 
@@ -568,7 +568,7 @@ void main() {
 
     test('should not apply the scope to non null event fields ', () async {
       final client = fixture.getSut(sendDefaultPii: true);
-      final scope = createScope(fixture.options);
+      final scope = await createScope(fixture.options);
 
       await client.captureEvent(event, scope: scope);
 
@@ -585,7 +585,7 @@ void main() {
 
     test('should apply the scope user to null event user fields ', () async {
       final client = fixture.getSut(sendDefaultPii: true);
-      final scope = createScope(fixture.options);
+      final scope = await createScope(fixture.options);
 
       await scope.setUser(SentryUser(id: '987'));
 
@@ -608,7 +608,7 @@ void main() {
 
     test('merge scope user and event user extra', () async {
       final client = fixture.getSut(sendDefaultPii: true);
-      final scope = createScope(fixture.options);
+      final scope = await createScope(fixture.options);
 
       await scope.setUser(
         SentryUser(