diff --git a/src/librustdoc/html/static/js/source-script.js b/src/librustdoc/html/static/js/source-script.js
index aaac878d3a37..58c036e0b3ca 100644
--- a/src/librustdoc/html/static/js/source-script.js
+++ b/src/librustdoc/html/static/js/source-script.js
@@ -205,6 +205,10 @@ const handleSourceHighlight = (function() {
 
     return ev => {
         let cur_line_id = parseInt(ev.target.id, 10);
+        // It can happen when clicking not on a line number span.
+        if (isNaN(cur_line_id)) {
+            return;
+        }
         ev.preventDefault();
 
         if (ev.shiftKey && prev_line_id) {