diff --git a/app/src/main/java/eu/faircode/email/FragmentCompose.java b/app/src/main/java/eu/faircode/email/FragmentCompose.java
index a2c5f5f2..3f960674 100644
--- a/app/src/main/java/eu/faircode/email/FragmentCompose.java
+++ b/app/src/main/java/eu/faircode/email/FragmentCompose.java
@@ -640,11 +640,9 @@ public class FragmentCompose extends FragmentEx {
             attachment.sequence = db.attachment().getAttachmentCount(draft.id) + 1;
             attachment.name = name;
 
-            String extension = null;
-            if (attachment.name != null) // External attach
-                extension = MimeTypeMap.getFileExtensionFromUrl(attachment.name.toLowerCase());
+            String extension = Helper.getExtension(attachment.name);
             if (extension != null)
-                attachment.type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);
+                attachment.type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension.toLowerCase());
             if (attachment.type == null)
                 attachment.type = "application/octet-stream";
 
diff --git a/app/src/main/java/eu/faircode/email/Helper.java b/app/src/main/java/eu/faircode/email/Helper.java
index 50fb88e7..11e17b25 100644
--- a/app/src/main/java/eu/faircode/email/Helper.java
+++ b/app/src/main/java/eu/faircode/email/Helper.java
@@ -205,6 +205,15 @@ public class Helper {
         }
     }
 
+    static String getExtension(String filename) {
+        if (filename == null)
+            return null;
+        int index = filename.lastIndexOf(".");
+        if (index < 0)
+            return null;
+        return filename.substring(index + 1);
+    }
+
     static String refreshToken(Context context, String type, String name, String current) {
         try {
             AccountManager am = AccountManager.get(context);
diff --git a/app/src/main/java/eu/faircode/email/MessageHelper.java b/app/src/main/java/eu/faircode/email/MessageHelper.java
index 579106ef..5c9e39e7 100644
--- a/app/src/main/java/eu/faircode/email/MessageHelper.java
+++ b/app/src/main/java/eu/faircode/email/MessageHelper.java
@@ -459,10 +459,10 @@ public class MessageHelper {
 
                 // Try to guess a better content type
                 // Sometimes PDF files are sent using the wrong type
-                if ("application/octet-stream".equals(attachment.type) && attachment.name != null) {
-                    String extension = MimeTypeMap.getFileExtensionFromUrl(attachment.name.toLowerCase());
+                if ("application/octet-stream".equals(attachment.type)) {
+                    String extension = Helper.getExtension(attachment.name);
                     if (extension != null) {
-                        String type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);
+                        String type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension.toLowerCase());
                         if (type != null) {
                             Log.w(Helper.TAG, "Guessing file=" + attachment.name + " type=" + type);
                             attachment.type = type;