diff --git a/all_test.go b/all_test.go
index dd8ae18..a024173 100644
--- a/all_test.go
+++ b/all_test.go
@@ -257,6 +257,9 @@ var libraryTable = []struct {
 
 	// Whitespace handling.
 	{" / descendant-or-self :: node() // child :: book / child :: * [ contains( . , '083' ) ] ", "0836217462"},
+
+	// Equals-off-by-one.
+	{"library/book[isbn='083621746']", exists(false)},
 }
 
 var libraryXml = []byte(`
diff --git a/parser.go b/parser.go
index 4b5c448..5ded228 100644
--- a/parser.go
+++ b/parser.go
@@ -104,7 +104,7 @@ func (node *Node) equals(s string) bool {
 	for i := node.pos; i < node.end; i++ {
 		if node.nodes[i].kind == textNode {
 			for _, c := range node.nodes[i].text {
-				if si > len(s) {
+				if si >= len(s) {
 					return false
 				}
 				if s[si] != c {