diff --git a/app/src/main/java/eu/faircode/email/MessageHelper.java b/app/src/main/java/eu/faircode/email/MessageHelper.java
index 8f263dfa09..a2387ffdf6 100644
--- a/app/src/main/java/eu/faircode/email/MessageHelper.java
+++ b/app/src/main/java/eu/faircode/email/MessageHelper.java
@@ -1224,15 +1224,16 @@ public class MessageHelper {
                     // For example, sometimes PDF files are sent as application/octet-stream
                     if (!apart.pgp) {
                         String extension = Helper.getExtension(apart.attachment.name);
-                        if (extension != null &&
-                                ("pdf".equals(extension.toLowerCase(Locale.ROOT)) ||
-                                        "application/octet-stream".equals(apart.attachment.type))) {
-                            String type = MimeTypeMap.getSingleton()
-                                    .getMimeTypeFromExtension(extension.toLowerCase(Locale.ROOT));
-                            if (type != null) {
-                                if (!type.equals(apart.attachment.type))
-                                    Log.w("Guessing file=" + apart.attachment.name + " type=" + type);
-                                apart.attachment.type = type;
+                        if (extension != null) {
+                            if ("application/zip".equals(apart.attachment.type) ||
+                                    "application/octet-stream".equals(apart.attachment.type)) {
+                                String type = MimeTypeMap.getSingleton()
+                                        .getMimeTypeFromExtension(extension.toLowerCase(Locale.ROOT));
+                                if (type != null) {
+                                    if (!type.equals(apart.attachment.type))
+                                        Log.w("Guessing file=" + apart.attachment.name + " type=" + type);
+                                    apart.attachment.type = type;
+                                }
                             }
                         }
                     }