diff --git a/sanitize/sanitize.go b/sanitize/sanitize.go
index aee7daa..544458a 100644
--- a/sanitize/sanitize.go
+++ b/sanitize/sanitize.go
@@ -2,9 +2,11 @@
 // the saved page is inert: a photograph, not a program.
 //
 // It parses with golang.org/x/net/html, walks the tree, and deletes scripts,
-// event handlers, javascript: URLs, and the dead preconnect/preload hints that
-// mean nothing offline — while leaving styles, images, fonts, forms, and all
-// semantic markup untouched so the layout survives intact.
+// event handlers, javascript: URLs, downlevel IE conditional comments (which
+// can smuggle a <script> past an element-only walk), and the dead
+// preconnect/preload hints that mean nothing offline — while leaving styles,
+// images, fonts, forms, and all semantic markup untouched so the layout
+// survives intact.
 package sanitize
 
 import (
@@ -31,13 +33,14 @@ type Options struct {
 
 // Report counts what was removed, for the run summary and for tests.
 type Report struct {
-	ScriptsRemoved     int
-	HandlersRemoved    int
-	NoscriptRemoved    int
-	NoscriptUnwrapped  int
-	JSURLsNeutralized  int
-	MetaRefreshRemoved int
-	DeadLinksRemoved   int
+	ScriptsRemoved      int
+	HandlersRemoved     int
+	NoscriptRemoved     int
+	NoscriptUnwrapped   int
+	JSURLsNeutralized   int
+	MetaRefreshRemoved  int
+	DeadLinksRemoved    int
+	CondCommentsRemoved int
 }
 
 // jsURLAttrs are attributes whose value may be a javascript: URL.
@@ -78,6 +81,18 @@ func clean(n *html.Node, opts Options, rep *Report) {
 	var next *html.Node
 	for c := n.FirstChild; c != nil; c = next {
 		next = c.NextSibling
+		if c.Type == html.CommentNode {
+			// A downlevel IE conditional comment (<!--[if lt IE 9]>...<![endif]-->)
+			// parses as one comment whose data holds raw markup — a <script src>
+			// among it. The element walk never sees that script, so drop the whole
+			// comment. Downlevel-revealed content lives in sibling nodes, not the
+			// comment data, so it is untouched.
+			if isConditionalComment(c.Data) {
+				n.RemoveChild(c)
+				rep.CondCommentsRemoved++
+			}
+			continue
+		}
 		if c.Type == html.ElementNode {
 			switch c.DataAtom {
 			case atom.Script:
@@ -175,6 +190,19 @@ func isDeadLink(n *html.Node) bool {
 	return false
 }
 
+// isConditionalComment reports whether a comment's data is a downlevel IE
+// conditional-comment marker. Both the downlevel-hidden form (the whole
+// "[if lt IE 9]>...<![endif]" in one comment) and the two markers of the
+// downlevel-revealed form ("[if gte IE 9]><!" and "<![endif]") match, so the
+// markers are stripped while any revealed content, which sits in sibling
+// nodes, stays.
+func isConditionalComment(data string) bool {
+	d := strings.TrimSpace(data)
+	return strings.HasPrefix(d, "[if") ||
+		strings.HasPrefix(d, "<![endif]") ||
+		strings.HasPrefix(d, "[endif]")
+}
+
 // unwrapNoscript replaces a <noscript> with its content. Because x/net/html
 // parses noscript content as raw text (scripting enabled), the text is
 // re-parsed as a fragment in the parent's context and spliced in before the
diff --git a/sanitize/sanitize_test.go b/sanitize/sanitize_test.go
index 90890a3..f663a12 100644
--- a/sanitize/sanitize_test.go
+++ b/sanitize/sanitize_test.go
@@ -107,6 +107,48 @@ func TestKeepNoscriptUnwraps(t *testing.T) {
 	}
 }
 
+func TestConditionalCommentScriptRemoved(t *testing.T) {
+	// A downlevel-hidden IE conditional comment hides a <script src> inside a
+	// single comment node, where an element-only walk never reaches it.
+	in := `<html><head>
+<!--[if lt IE 9]><script src="//oss.maxcdn.com/html5shiv/3.7.2/html5shiv.min.js"></script><![endif]-->
+</head><body><p>real</p></body></html>`
+	out, rep, err := Strip([]byte(in), Options{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	s := string(out)
+	if strings.Contains(s, "<script") || strings.Contains(s, "html5shiv") {
+		t.Errorf("conditional-comment script survived:\n%s", s)
+	}
+	if strings.Contains(s, "[if lt IE 9]") {
+		t.Errorf("conditional comment survived:\n%s", s)
+	}
+	if rep.CondCommentsRemoved != 1 {
+		t.Errorf("CondCommentsRemoved = %d, want 1", rep.CondCommentsRemoved)
+	}
+	if !strings.Contains(s, "<p>real</p>") {
+		t.Errorf("real content must survive:\n%s", s)
+	}
+}
+
+func TestConditionalCommentRevealedContentKept(t *testing.T) {
+	// The downlevel-revealed form shows its content to non-IE browsers; the
+	// content lives in sibling nodes, so only the two markers are stripped.
+	in := `<html><body><!--[if gte IE 9]><!--><span class="modern">keep me</span><!--<![endif]--></body></html>`
+	out, _, err := Strip([]byte(in), Options{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	s := string(out)
+	if !strings.Contains(s, `<span class="modern">keep me</span>`) {
+		t.Errorf("revealed content was dropped:\n%s", s)
+	}
+	if strings.Contains(s, "[if") || strings.Contains(s, "<![endif]") {
+		t.Errorf("conditional markers survived:\n%s", s)
+	}
+}
+
 func TestKeepMetaRefreshPlain(t *testing.T) {
 	in := `<html><head><meta http-equiv="refresh" content="5;url=/next"></head><body></body></html>`
 	out, _, err := Strip([]byte(in), Options{KeepMetaRefresh: true})
