diff --git a/inline.go b/inline.go
index 1070762..db02091 100644
--- a/inline.go
+++ b/inline.go
@@ -620,7 +620,7 @@ func autoLink(p *parser, out *bytes.Buffer, data []byte, offset int) int {
 
 	// scan backward for a word boundary
 	rewind := 0
-	for offset-rewind > 0 && rewind <= 7 && isalnum(data[offset-rewind-1]) {
+	for offset-rewind > 0 && rewind <= 7 && isletter(data[offset-rewind-1]) {
 		rewind++
 	}
 	if rewind > 6 { // longest supported protocol is "mailto" which has 6 letters
diff --git a/inline_test.go b/inline_test.go
index f621529..60f764c 100644
--- a/inline_test.go
+++ b/inline_test.go
@@ -462,6 +462,45 @@ func TestTags(t *testing.T) {
 
 func TestAutoLink(t *testing.T) {
 	var tests = []string{
+		"http://foo.com/\n",
+		"<p><a href=\"http://foo.com/\">http://foo.com/</a></p>\n",
+
+		"1 http://foo.com/\n",
+		"<p>1 <a href=\"http://foo.com/\">http://foo.com/</a></p>\n",
+
+		"1http://foo.com/\n",
+		"<p>1<a href=\"http://foo.com/\">http://foo.com/</a></p>\n",
+
+		"1.http://foo.com/\n",
+		"<p>1.<a href=\"http://foo.com/\">http://foo.com/</a></p>\n",
+
+		"1. http://foo.com/\n",
+		"<ol>\n<li><a href=\"http://foo.com/\">http://foo.com/</a></li>\n</ol>\n",
+
+		"-http://foo.com/\n",
+		"<p>-<a href=\"http://foo.com/\">http://foo.com/</a></p>\n",
+
+		"- http://foo.com/\n",
+		"<ul>\n<li><a href=\"http://foo.com/\">http://foo.com/</a></li>\n</ul>\n",
+
+		"_http://foo.com/\n",
+		"<p>_<a href=\"http://foo.com/\">http://foo.com/</a></p>\n",
+
+		"令狐http://foo.com/\n",
+		"<p>令狐<a href=\"http://foo.com/\">http://foo.com/</a></p>\n",
+
+		"令狐 http://foo.com/\n",
+		"<p>令狐 <a href=\"http://foo.com/\">http://foo.com/</a></p>\n",
+
+		"ahttp://foo.com/\n",
+		"<p>ahttp://foo.com/</p>\n",
+
+		">http://foo.com/\n",
+		"<blockquote>\n<p><a href=\"http://foo.com/\">http://foo.com/</a></p>\n</blockquote>\n",
+
+		"> http://foo.com/\n",
+		"<blockquote>\n<p><a href=\"http://foo.com/\">http://foo.com/</a></p>\n</blockquote>\n",
+
 		"go to <http://foo.com/>\n",
 		"<p>go to <a href=\"http://foo.com/\">http://foo.com/</a></p>\n",
 
diff --git a/markdown.go b/markdown.go
index 77e93e8..322300f 100644
--- a/markdown.go
+++ b/markdown.go
@@ -685,10 +685,15 @@ func isspace(c byte) bool {
 	return c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == '\f' || c == '\v'
 }
 
+// Test if a character is letter.
+func isletter(c byte) bool {
+	return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
+}
+
 // Test if a character is a letter or a digit.
 // TODO: check when this is looking for ASCII alnum and when it should use unicode
 func isalnum(c byte) bool {
-	return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
+	return (c >= '0' && c <= '9') || isletter(c)
 }
 
 // Replace tab characters with spaces, aligning to the next TAB_SIZE column.