diff --git a/src/lib.rs b/src/lib.rs
index a13de4035..06f676298 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,8 +1,6 @@
 #![forbid(unsafe_code)]
 #![deny(clippy::correctness, missing_debug_implementations, clippy::all)]
 #![allow(clippy::match_bool)]
-#![feature(ptr_wrapping_offset_from)]
-#![feature(drain_filter)]
 
 #[macro_use]
 extern crate failure_derive;
diff --git a/src/mimeparser.rs b/src/mimeparser.rs
index 36a21cd62..39814361c 100644
--- a/src/mimeparser.rs
+++ b/src/mimeparser.rs
@@ -178,10 +178,16 @@ impl<'a> MimeMessage<'a> {
     #[allow(clippy::cognitive_complexity)]
     fn parse_headers(&mut self) -> Result<()> {
         if self.get(HeaderDef::AutocryptSetupMessage).is_some() {
-            self.parts.drain_filter(|part| {
-                part.mimetype.is_some()
-                    && part.mimetype.as_ref().unwrap().as_ref() != MIME_AC_SETUP_FILE
-            });
+            self.parts = self
+                .parts
+                .iter()
+                .filter(|part| {
+                    part.mimetype.is_none()
+                        || part.mimetype.as_ref().unwrap().as_ref() == MIME_AC_SETUP_FILE
+                })
+                .cloned()
+                .collect();
+
             if self.parts.len() == 1 {
                 self.is_system_message = SystemMessage::AutocryptSetupMessage;
             } else {