diff --git a/owasp-java-html-sanitizer/src/main/java/org/owasp/html/HtmlStreamRenderer.java b/owasp-java-html-sanitizer/src/main/java/org/owasp/html/HtmlStreamRenderer.java
index 7e657ee1..7d7a24d2 100644
--- a/owasp-java-html-sanitizer/src/main/java/org/owasp/html/HtmlStreamRenderer.java
+++ b/owasp-java-html-sanitizer/src/main/java/org/owasp/html/HtmlStreamRenderer.java
@@ -393,9 +393,11 @@ static boolean isValidHtmlName(String name) {
           if (i == 0 || i + 1 == n) { return false; }
           break;
         case '-':
-        case '_':
           if (i == 0 || i + 1 == n) { return false; }
           break;
+        case '_':
+          if (i + 1 == n) { return false; }
+          break;
         default:
           if (ch <= '9') {
             if (i == 0 || ch < '0') { return false; }
diff --git a/owasp-java-html-sanitizer/src/test/java/org/owasp/html/HtmlSanitizerTest.java b/owasp-java-html-sanitizer/src/test/java/org/owasp/html/HtmlSanitizerTest.java
index 1ff169df..b6693349 100644
--- a/owasp-java-html-sanitizer/src/test/java/org/owasp/html/HtmlSanitizerTest.java
+++ b/owasp-java-html-sanitizer/src/test/java/org/owasp/html/HtmlSanitizerTest.java
@@ -195,6 +195,13 @@ public static final void testEmptyAndValuelessAttributes() {
         sanitize("<input checked type=checkbox id=\"\" class=>"));
   }
 
+  @Test
+  public final void testAllowedAttributes() {
+    assertEquals(
+            "<div __foo=\"__foo\" __bar=\"foo\" foo-bar=\"foo-bar\"></div>",
+            sanitize("<div __foo __bar=\"foo\" foo-bar></div>"));
+  }
+
   @Test
   public static final void testSgmlShortTags() {
     // We make no attempt to correctly handle SGML short tags since they are
@@ -471,7 +478,8 @@ public void handle(String errorMessage) {
            "ol", "p", "span", "ul", "noscript", "noframes", "noembed", "noxss")
        // And these attributes.
        .allowAttributes(
-           "dir", "checked", "class", "href", "id", "target", "title", "type")
+           "dir", "checked", "class", "href", "id", "target", "title", "type",
+               "__foo", "__bar", "foo-bar")
        .globally()
        // Cleanup IDs and CLASSes and prefix them with p- to move to a separate
        // name-space.