diff --git a/src/document.c b/src/document.c
index 613fd6df..27c17b23 100644
--- a/src/document.c
+++ b/src/document.c
@@ -2752,6 +2752,10 @@ hoedown_document_new(
 
 	memset(doc->active_char, 0x0, 256);
 
+	if (extensions & HOEDOWN_EXT_UNDERLINE && doc->md.underline) {
+		doc->active_char['_'] = MD_CHAR_EMPHASIS;
+	}
+
 	if (doc->md.emphasis || doc->md.double_emphasis || doc->md.triple_emphasis) {
 		doc->active_char['*'] = MD_CHAR_EMPHASIS;
 		doc->active_char['_'] = MD_CHAR_EMPHASIS;
@@ -2767,7 +2771,7 @@ hoedown_document_new(
 	if (doc->md.linebreak)
 		doc->active_char['\n'] = MD_CHAR_LINEBREAK;
 
-	if (doc->md.image || doc->md.link)
+	if (doc->md.image || doc->md.link || doc->md.footnotes || doc->md.footnote_ref)
 		doc->active_char['['] = MD_CHAR_LINK;
 
 	doc->active_char['<'] = MD_CHAR_LANGLE;
diff --git a/src/html_smartypants.c b/src/html_smartypants.c
index bbe4fc50..b0904da7 100644
--- a/src/html_smartypants.c
+++ b/src/html_smartypants.c
@@ -313,6 +313,16 @@ smartypants_cb__ltag(hoedown_buffer *ob, struct smartypants_data *smrt, uint8_t
 
 	size_t tag, i = 0;
 
+	/* This is a comment. Copy everything verbatim until --> or EOF is seen. */
+	if (i + 4 < size && memcmp(text, "<!--", 4) == 0) {
+		i += 4;
+		while (i + 3 < size && memcmp(text + i, "-->",  3) != 0)
+			i++;
+		i += 3;
+		hoedown_buffer_put(ob, text, i + 1);
+		return i;
+	}
+
 	while (i < size && text[i] != '>')
 		i++;
 
diff --git a/test/Tests/Underline.html b/test/Tests/Underline.html
new file mode 100644
index 00000000..c2a8bbad
--- /dev/null
+++ b/test/Tests/Underline.html
@@ -0,0 +1 @@
+<p>This <u>underline</u> will work.</p>
diff --git a/test/Tests/Underline.text b/test/Tests/Underline.text
new file mode 100644
index 00000000..8068546c
--- /dev/null
+++ b/test/Tests/Underline.text
@@ -0,0 +1 @@
+This _underline_ will work.
diff --git a/test/config.json b/test/config.json
index b6ecb551..d3e170e8 100644
--- a/test/config.json
+++ b/test/config.json
@@ -101,6 +101,11 @@
             "input": "Tests/Math.text",
             "output": "Tests/Math.html",
             "flags": ["--math"]
+        },
+        {
+            "input": "Tests/Underline.text",
+            "output": "Tests/Underline.html",
+            "flags": ["--underline"]
         }
     ]
 }