diff --git a/core/src/main/java/org/eclipse/angus/mail/util/BASE64DecoderStream.java b/core/src/main/java/org/eclipse/angus/mail/util/BASE64DecoderStream.java
index 52478c9e..af64bc36 100644
--- a/core/src/main/java/org/eclipse/angus/mail/util/BASE64DecoderStream.java
+++ b/core/src/main/java/org/eclipse/angus/mail/util/BASE64DecoderStream.java
@@ -202,7 +202,7 @@ public int available() throws IOException {
     private final static byte[] pem_convert_array = new byte[256];
 
     static {
-        for (int i = 0; i < 255; i++)
+        for (int i = 0; i < pem_convert_array.length; i++)
             pem_convert_array[i] = -1;
         for (int i = 0; i < pem_array.length; i++)
             pem_convert_array[pem_array[i]] = (byte) i;
diff --git a/providers/angus-mail/src/test/java/org/eclipse/angus/mail/util/BASE64Test.java b/providers/angus-mail/src/test/java/org/eclipse/angus/mail/util/BASE64Test.java
index eee00b7f..e0020fea 100644
--- a/providers/angus-mail/src/test/java/org/eclipse/angus/mail/util/BASE64Test.java
+++ b/providers/angus-mail/src/test/java/org/eclipse/angus/mail/util/BASE64Test.java
@@ -278,6 +278,37 @@ public void testReadZeroBytes() throws Exception {
         //assertArrayEquals(decoded, result);
     }
 
+    /**
+     * A byte that is not part of the base64 alphabet must be skipped,
+     * the same way whitespace is.  The 0xFF byte in particular must not
+     * be treated as a valid character.
+     */
+    @Test
+    public void testNonBase64ByteSkipped() throws IOException {
+        // "TWFu" is the base64 encoding of "Man"; inject a stray 0xFF byte
+        byte[] clean = new byte[]{'T', 'W', 'F', 'u'};
+        byte[] withStray = new byte[]{'T', 'W', (byte) 0xFF, 'F', 'u'};
+
+        byte[] expected = readFully(new BASE64DecoderStream(
+                new ByteArrayInputStream(clean)));
+        byte[] actual = readFully(new BASE64DecoderStream(
+                new ByteArrayInputStream(withStray)));
+
+        Assert.assertArrayEquals("0xFF must be ignored like whitespace",
+                expected, actual);
+        // cross-check against a conformant decoder that ignores non-alphabet bytes
+        Assert.assertArrayEquals("must match JDK MIME decoder",
+                Base64.getMimeDecoder().decode(withStray), actual);
+    }
+
+    private static byte[] readFully(InputStream in) throws IOException {
+        ByteArrayOutputStream bos = new ByteArrayOutputStream();
+        int b;
+        while ((b = in.read()) != -1)
+            bos.write(b);
+        return bos.toByteArray();
+    }
+
     /**
      * Fill the buffer from the stream.
      */