diff --git a/cms/src/builder.rs b/cms/src/builder.rs
index b4f2e2a43..b4abec592 100644
--- a/cms/src/builder.rs
+++ b/cms/src/builder.rs
@@ -783,15 +783,11 @@ where
         let cek_byte_count: u8 = content_encryption_key.len().try_into().map_err(|_| {
             Error::Builder("Content encryption key length must not exceed 255".to_string())
         })?;
-        let mut check_value = vec![
-            0xff ^ content_encryption_key[0],
-            0xff ^ content_encryption_key[1],
-            0xff ^ content_encryption_key[2],
-        ];
-
-        let mut wrapped_cek: Vec<u8> = Vec::new();
+        let mut wrapped_cek: Vec<u8> = Vec::with_capacity(4 + padding_length);
         wrapped_cek.insert(0, cek_byte_count);
-        wrapped_cek.append(&mut check_value);
+        wrapped_cek.insert(0xff ^ content_encryption_key[0]);
+        wrapped_cek.insert(0xff ^ content_encryption_key[1]);
+        wrapped_cek.insert(0xff ^ content_encryption_key[2]);
         if padding_length > 0 {
             let mut padding = vec![0_u8; padding_length];
             self.rng.fill_bytes(padding.as_mut_slice());