diff --git a/tests/src/com/fsck/k9/mail/internet/DecoderUtilTest.java b/tests/src/com/fsck/k9/mail/internet/DecoderUtilTest.java
new file mode 100644
index 000000000..e9c7d62c6
--- /dev/null
+++ b/tests/src/com/fsck/k9/mail/internet/DecoderUtilTest.java
@@ -0,0 +1,113 @@
+package com.fsck.k9.mail.internet;
+
+import junit.framework.TestCase;
+
+public class DecoderUtilTest extends TestCase {
+
+    protected void setUp() throws Exception {
+        super.setUp();
+    }
+
+    protected void tearDown() throws Exception {
+        super.tearDown();
+    }
+
+    public void testDecodeEncodedWords() {
+        String body, expect;
+        MimeMessage message;
+
+        body = "abc";
+        expect = "abc";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=?us-ascii?q?abc?=";
+        expect = "abc";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=?";
+        expect = "=?";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=??";
+        expect = "=??";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=???";
+        expect = "=???";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=????";
+        expect = "=????";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=????=";
+        expect = "=????=";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=??q??=";
+        expect = "=??q??=";;
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=??q?a?=";
+        expect = "=??q?a?=";
+        //expect = "a";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=??=";
+        expect = "=??=";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=?x?=";
+        expect = "=?x?=";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=?x??=";
+        expect = "=?x??=";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=?x?q?=";
+        expect = "=?x?q?=";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=?x?q??=";
+        expect = "=?x?q??=";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=?x?q?X?=";
+        expect = "=?x?q?X?=";
+        //expect = "X";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        // invalid base64 string
+        body = "=?us-ascii?b?abc?=";
+        expect = "";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        // broken encoded header
+        body = "=?us-ascii?q?abc?= =?";
+        expect = "abc =?";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+
+        body = "=?x?= =?";
+        expect = "=?x?= =?";
+        message = null;
+        assertEquals(expect, DecoderUtil.decodeEncodedWords(body, message));
+    }
+}