diff --git a/commons-fileupload2-core/src/main/java/org/apache/commons/fileupload2/core/MimeUtils.java b/commons-fileupload2-core/src/main/java/org/apache/commons/fileupload2/core/MimeUtils.java
index 37f96010f..0cd0e8473 100644
--- a/commons-fileupload2-core/src/main/java/org/apache/commons/fileupload2/core/MimeUtils.java
+++ b/commons-fileupload2-core/src/main/java/org/apache/commons/fileupload2/core/MimeUtils.java
@@ -224,10 +224,10 @@ private static String decodeWord(final String word) throws ParseException, Unsup
 
             final var encodedData = encodedText.getBytes(StandardCharsets.US_ASCII);
 
-            // Base64 encoded?
-            if (encoding.equals(BASE64_ENCODING_MARKER)) {
+            // Base64 encoded? RFC 2047 section 2 defines the encoding token as case-independent, so 'b' and 'q' are also valid.
+            if (encoding.equalsIgnoreCase(BASE64_ENCODING_MARKER)) {
                 out.write(Base64.getMimeDecoder().decode(encodedData));
-            } else if (encoding.equals(QUOTEDPRINTABLE_ENCODING_MARKER)) { // maybe quoted printable.
+            } else if (encoding.equalsIgnoreCase(QUOTEDPRINTABLE_ENCODING_MARKER)) { // maybe quoted printable.
                 QuotedPrintableDecoder.decode(encodedData, out);
             } else {
                 throw new UnsupportedEncodingException("Unknown RFC 2047 encoding: " + encoding);
diff --git a/commons-fileupload2-core/src/test/java/org/apache/commons/fileupload2/core/MimeUtilityTestCase.java b/commons-fileupload2-core/src/test/java/org/apache/commons/fileupload2/core/MimeUtilityTestCase.java
index 9186b9b6c..62867c5d3 100644
--- a/commons-fileupload2-core/src/test/java/org/apache/commons/fileupload2/core/MimeUtilityTestCase.java
+++ b/commons-fileupload2-core/src/test/java/org/apache/commons/fileupload2/core/MimeUtilityTestCase.java
@@ -54,11 +54,23 @@ void testDecodeUtf8Base64Encoded() throws Exception {
         assertEncoded(" h\u00e9! \u00e0\u00e8\u00f4u !!!", "=?UTF-8?B?IGjDqSEgw6DDqMO0dSAhISE=?=");
     }
 
+    @Test
+    void testDecodeUtf8Base64EncodedLowerCaseMarker() throws Exception {
+        // RFC 2047 section 2: the encoding token is case-independent, so 'b' decodes like 'B'.
+        assertEncoded(" h\u00e9! \u00e0\u00e8\u00f4u !!!", "=?UTF-8?b?IGjDqSEgw6DDqMO0dSAhISE=?=");
+    }
+
     @Test
     void testDecodeUtf8QuotedPrintableEncoded() throws Exception {
         assertEncoded(" h\u00e9! \u00e0\u00e8\u00f4u !!!", "=?UTF-8?Q?_h=C3=A9!_=C3=A0=C3=A8=C3=B4u_!!!?=");
     }
 
+    @Test
+    void testDecodeUtf8QuotedPrintableEncodedLowerCaseMarker() throws Exception {
+        // RFC 2047 section 2: the encoding token is case-independent, so 'q' decodes like 'Q'.
+        assertEncoded(" h\u00e9! \u00e0\u00e8\u00f4u !!!", "=?UTF-8?q?_h=C3=A9!_=C3=A0=C3=A8=C3=B4u_!!!?=");
+    }
+
     @Test
     void testNoNeedToDecode() throws Exception {
         assertEncoded("abc", "abc");