diff --git a/src/mimeparser.rs b/src/mimeparser.rs
index 094c51975..9d952612b 100644
--- a/src/mimeparser.rs
+++ b/src/mimeparser.rs
@@ -1517,6 +1517,16 @@ mod tests {
         assert_eq!(filename, Some("Maßn'ah'men Okt. 2020.html".to_string()))
     }
 
+    #[test]
+    fn test_get_attachment_filename_encoded_words_bad_delimiter() {
+        let mail = load_mail_with_attachment(include_bytes!(
+            "../test-data/message/attach_filename_encoded_words_bad_delimiter.eml"
+        ));
+        let filename = get_attachment_filename(&mail.subparts[1]).unwrap();
+        // not decoded as a space is missing after encoded-words part
+        assert_eq!(filename, Some("=?utf-8?q?foo?=.bar".to_string()))
+    }
+
     #[test]
     fn test_get_attachment_filename_combined() {
         // test that if `filename` and `filename*0` are given, the filename is not doubled
diff --git a/test-data/message/attach_filename_encoded_words_bad_delimiter.eml b/test-data/message/attach_filename_encoded_words_bad_delimiter.eml
new file mode 100644
index 000000000..a1ae8207c
--- /dev/null
+++ b/test-data/message/attach_filename_encoded_words_bad_delimiter.eml
@@ -0,0 +1,29 @@
+Subject: Test encoded-words filenames
+Message-ID: 123456@testrun.org
+Date: Sat, 07 Dec 2019 19:00:27 +0000
+Chat-Version: 1.0
+To: recp@testrun.org
+From: sender@testrun.org
+Content-Type: multipart/mixed; boundary="==BREAK=="
+
+
+--==BREAK==
+Content-Type: text/plain; charset=utf-8
+
+there MUST be a space between encoded words and plain text,
+if there is none, decoding should return the original string
+https://tools.ietf.org/html/rfc2047 5.1:
+
+"Ordinary ASCII text and 'encoded-word's may appear together in the
+same header field.  However, an 'encoded-word' that appears in a
+header field defined as '*text' MUST be separated from any adjacent
+'encoded-word' or 'text' by 'linear-white-space'."
+
+--==BREAK==
+Content-Type: text/html
+Content-Disposition: attachment; filename="=?utf-8?q?foo?=.bar";
+Content-Transfer-Encoding: base64
+
+PGh0bWw+PGJvZHk+dGV4dDwvYm9keT5kYXRh
+
+--==BREAK==--