diff --git a/src/engine/rfc822/rfc822-message.vala b/src/engine/rfc822/rfc822-message.vala
index 227be19..fb665da 100644
--- a/src/engine/rfc822/rfc822-message.vala
+++ b/src/engine/rfc822/rfc822-message.vala
@@ -484,6 +484,9 @@ public class Geary.RFC822.Message : BaseObject {
             return false;
         }
         
+        if (disposition == null)
+            return;
+        
         // Hand off to the replacer for processing
         if (replacer == null)
             return false;
