diff --git a/app/email_utils.py b/app/email_utils.py
index f5d1a19b..70cec703 100644
--- a/app/email_utils.py
+++ b/app/email_utils.py
@@ -951,6 +951,8 @@ def add_header(msg: Message, text_header, html_header=None) -> Message:
         for part in msg.get_payload():
             if isinstance(part, Message):
                 new_parts.append(add_header(part, text_header, html_header))
+            elif isinstance(part, str):
+                new_parts.append(MIMEText(part))
             else:
                 new_parts.append(part)
         clone_msg = copy(msg)
diff --git a/tests/example_emls/email_to_pgp_encrypt.eml b/tests/example_emls/email_to_pgp_encrypt.eml
new file mode 100644
index 00000000..fb3b969f
--- /dev/null
+++ b/tests/example_emls/email_to_pgp_encrypt.eml
@@ -0,0 +1,27 @@
+From: {{sender_address}}
+To: {{recipient_address}}
+Subject: Test subject
+Content-Type: multipart/alternative; boundary="MLF8fvg556fdhFDH7=_?:
+
+--MLF8fvg556fdhFDH7=_?:
+Content-Type: text/plain;
+    charset="utf-8"
+Content-Transfer-Encoding: quoted-printable
+
+*************************************************************************
+
+This five-part limited series, based on the brilliant graphic novel by Me
+
+--MLF8fvg556fdhFDH7=_?:
+Content-Type: text/html;
+     charset="utf-8"
+Content-Transfer-Encoding: 8bit
+--MLF8fvg556fdhFDH7=_?:
+Content-Type: text/plain;
+    charset="utf-8"
+Content-Transfer-Encoding: quoted-printable
+
+*************************************************************************
+*************************************************************************
+
+
diff --git a/tests/handler/test_encrypt_pgp.py b/tests/handler/test_encrypt_pgp.py
new file mode 100644
index 00000000..d265a844
--- /dev/null
+++ b/tests/handler/test_encrypt_pgp.py
@@ -0,0 +1,33 @@
+from aiosmtpd.smtp import Envelope
+
+import email_handler
+from app.config import get_abs_path
+from app.db import Session
+from app.pgp_utils import load_public_key
+from tests.utils import create_new_user, load_eml_file, random_email
+
+from app.models import Alias
+
+
+def test_encrypt_with_pgp():
+    user = create_new_user()
+    pgp_public_key = open(get_abs_path("local_data/public-pgp.asc")).read()
+    mailbox = user.default_mailbox
+    mailbox.pgp_public_key = pgp_public_key
+    mailbox.generic_subject = True
+    mailbox.pgp_finger_print = load_public_key(pgp_public_key)
+    alias = Alias.create_new_random(user)
+    Session.flush()
+    sender_address = random_email()
+    msg = load_eml_file(
+        "email_to_pgp_encrypt.eml",
+        {
+            "sender_address": sender_address,
+            "recipient_address": alias.email,
+        },
+    )
+    envelope = Envelope()
+    envelope.mail_from = sender_address
+    envelope.rcpt_tos = [alias.email]
+    result = email_handler.MailHandler()._handle(envelope, msg)
+    assert result is not None
diff --git a/tests/test_email_utils.py b/tests/test_email_utils.py
index bc36edaf..749603a7 100644
--- a/tests/test_email_utils.py
+++ b/tests/test_email_utils.py
@@ -810,7 +810,7 @@ def test_add_header_multipart_with_invalid_part():
         if i < 2:
             assert part.get_payload().index("INJECT") > -1
         else:
-            assert part == "invalid"
+            assert part.get_payload() == "invalid"
 
 
 def test_sl_formataddr():