diff --git a/app/src/main/java/eu/faircode/email/Core.java b/app/src/main/java/eu/faircode/email/Core.java
index 354bfa391f..173ac301e8 100644
--- a/app/src/main/java/eu/faircode/email/Core.java
+++ b/app/src/main/java/eu/faircode/email/Core.java
@@ -2911,7 +2911,7 @@ class Core {
                         ifolder.setFlags(list.toArray(new Message[0]), flags, true);
                     } catch (MessagingException ex) {
                         Log.w(ex);
-                        for (Message imessage : list)
+                        for (Message imessage : new ArrayList<>(list))
                             try {
                                 imessage.setFlag(Flags.Flag.DELETED, true);
                             } catch (MessagingException mex) {