diff --git a/app/src/main/java/eu/faircode/email/ActivityView.java b/app/src/main/java/eu/faircode/email/ActivityView.java
index 2304583fe6..0ade983dba 100644
--- a/app/src/main/java/eu/faircode/email/ActivityView.java
+++ b/app/src/main/java/eu/faircode/email/ActivityView.java
@@ -948,9 +948,12 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
                 DB db = DB.getInstance(context);
 
                 // Find encrypted data
+                boolean found = false;
                 List<EntityAttachment> attachments = db.attachment().getAttachments(id);
                 for (EntityAttachment attachment : attachments)
                     if (attachment.available && "encrypted.asc".equals(attachment.name)) {
+                        found = true;
+
                         // Serialize encrypted data
                         FileInputStream encrypted = new FileInputStream(EntityAttachment.getFile(context, attachment.id));
                         ByteArrayOutputStream decrypted = new ByteArrayOutputStream();
@@ -1008,6 +1011,9 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
                         break;
                     }
 
+                if (!found)
+                    throw new IllegalArgumentException(getString(R.string.title_not_encrypted));
+
                 return null;
             }
 
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 8ee37ef38d..96b8f7db80 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -239,6 +239,7 @@
     <string name="title_encrypt">Encrypt</string>
     <string name="title_decrypt">Decrypt</string>
     <string name="title_no_openpgp">OpenKeychain not found</string>
+    <string name="title_not_encrypted">Message is not encrypted</string>
 
     <string name="title_search">Search</string>
     <string name="title_search_hint">Search on server</string>