diff --git a/block.go b/block.go
index b7d870c..23a693c 100644
--- a/block.go
+++ b/block.go
@@ -15,7 +15,7 @@ package blackfriday
 
 import (
 	"bytes"
-	"unicode"
+	"github.com/shurcooL/go/github_flavored_markdown/sanitized_anchor_name"
 )
 
 // Parse block-level data.
@@ -227,7 +227,7 @@ func (p *parser) prefixHeader(out *bytes.Buffer, data []byte) int {
 	}
 	if end > i {
 		if id == "" && p.flags&EXTENSION_AUTO_HEADER_IDS != 0 {
-			id = createSanitizedAnchorName(string(data[i:end]))
+			id = sanitized_anchor_name.Create(string(data[i:end]))
 		}
 		work := func() bool {
 			p.inline(out, data[i:end])
@@ -1276,7 +1276,7 @@ func (p *parser) paragraph(out *bytes.Buffer, data []byte) int {
 
 				id := ""
 				if p.flags&EXTENSION_AUTO_HEADER_IDS != 0 {
-					id = createSanitizedAnchorName(string(data[prev:eol]))
+					id = sanitized_anchor_name.Create(string(data[prev:eol]))
 				}
 
 				p.r.Header(out, work, level, id)
@@ -1325,16 +1325,3 @@ func (p *parser) paragraph(out *bytes.Buffer, data []byte) int {
 	p.renderParagraph(out, data[:i])
 	return i
 }
-
-func createSanitizedAnchorName(text string) string {
-	var anchorName []rune
-	for _, r := range []rune(text) {
-		switch {
-		case r == ' ':
-			anchorName = append(anchorName, '-')
-		case unicode.IsLetter(r) || unicode.IsNumber(r):
-			anchorName = append(anchorName, unicode.ToLower(r))
-		}
-	}
-	return string(anchorName)
-}
diff --git a/block_test.go b/block_test.go
index de77aa9..1c4f50a 100644
--- a/block_test.go
+++ b/block_test.go
@@ -275,10 +275,27 @@ func TestPrefixAutoHeaderIdExtension(t *testing.T) {
 		"*   List\n    * Nested list\n    # Nested header\n",
 		"<ul>\n<li><p>List</p>\n\n<ul>\n<li><p>Nested list</p>\n\n" +
 			"<h1 id=\"nested-header\">Nested header</h1></li>\n</ul></li>\n</ul>\n",
+
+		"# Header\n\n# Header\n",
+		"<h1 id=\"header\">Header</h1>\n\n<h1 id=\"header-1\">Header</h1>\n",
+
+		"# Header 1\n\n# Header 1",
+		"<h1 id=\"header-1\">Header 1</h1>\n\n<h1 id=\"header-1-1\">Header 1</h1>\n",
+
+		"# Header\n\n# Header 1\n\n# Header\n\n# Header",
+		"<h1 id=\"header\">Header</h1>\n\n<h1 id=\"header-1\">Header 1</h1>\n\n<h1 id=\"header-1-1\">Header</h1>\n\n<h1 id=\"header-1-2\">Header</h1>\n",
 	}
 	doTestsBlock(t, tests, EXTENSION_AUTO_HEADER_IDS)
 }
 
+func TestPrefixMultipleHeaderExtensions(t *testing.T) {
+	var tests = []string{
+		"# Header\n\n# Header {#header}\n\n# Header 1",
+		"<h1 id=\"header\">Header</h1>\n\n<h1 id=\"header-1\">Header</h1>\n\n<h1 id=\"header-1-1\">Header 1</h1>\n",
+	}
+	doTestsBlock(t, tests, EXTENSION_AUTO_HEADER_IDS|EXTENSION_HEADER_IDS)
+}
+
 func TestUnderlineHeaders(t *testing.T) {
 	var tests = []string{
 		"Header 1\n========\n",
@@ -369,6 +386,12 @@ func TestUnderlineHeadersAutoIDs(t *testing.T) {
 
 		"Double underline\n=====\n=====\n",
 		"<h1 id=\"double-underline\">Double underline</h1>\n\n<p>=====</p>\n",
+
+		"Header\n======\n\nHeader\n======\n",
+		"<h1 id=\"header\">Header</h1>\n\n<h1 id=\"header-1\">Header</h1>\n",
+
+		"Header 1\n========\n\nHeader 1\n========\n",
+		"<h1 id=\"header-1\">Header 1</h1>\n\n<h1 id=\"header-1-1\">Header 1</h1>\n",
 	}
 	doTestsBlock(t, tests, EXTENSION_AUTO_HEADER_IDS)
 }
diff --git a/html.go b/html.go
index a85f918..a552508 100644
--- a/html.go
+++ b/html.go
@@ -81,6 +81,9 @@ type Html struct {
 	currentLevel int
 	toc          *bytes.Buffer
 
+	// Track header IDs to prevent ID collision in a single generation.
+	headerIDs map[string]int
+
 	smartypants *smartypantsRenderer
 }
 
@@ -123,6 +126,8 @@ func HtmlRendererWithParameters(flags int, title string,
 		currentLevel: 0,
 		toc:          new(bytes.Buffer),
 
+		headerIDs: make(map[string]int),
+
 		smartypants: smartypants(flags),
 	}
 }
@@ -190,11 +195,12 @@ func (options *Html) Header(out *bytes.Buffer, text func() bool, level int, id s
 	marker := out.Len()
 	doubleSpace(out)
 
+	if id == "" && options.flags&HTML_TOC != 0 {
+		id = fmt.Sprintf("toc_%d", options.headerCount)
+	}
+
 	if id != "" {
-		out.WriteString(fmt.Sprintf("<h%d id=\"%s\">", level, id))
-	} else if options.flags&HTML_TOC != 0 {
-		// headerCount is incremented in htmlTocHeader
-		out.WriteString(fmt.Sprintf("<h%d id=\"toc_%d\">", level, options.headerCount))
+		out.WriteString(fmt.Sprintf("<h%d id=\"%s\">", level, options.ensureUniqueHeaderID(id)))
 	} else {
 		out.WriteString(fmt.Sprintf("<h%d>", level))
 	}
@@ -853,3 +859,22 @@ func isRelativeLink(link []byte) (yes bool) {
 	}
 	return
 }
+
+func (options *Html) ensureUniqueHeaderID(id string) string {
+	for count, found := options.headerIDs[id]; found; count, found = options.headerIDs[id] {
+		tmp := fmt.Sprintf("%s-%d", id, count+1)
+
+		if _, tmpFound := options.headerIDs[tmp]; !tmpFound {
+			options.headerIDs[id] = count + 1
+			id = tmp
+		} else {
+			id = id + "-1"
+		}
+	}
+
+	if _, found := options.headerIDs[id]; !found {
+		options.headerIDs[id] = 0
+	}
+
+	return id
+}