diff --git a/modules/domQueries/scope.js b/modules/domQueries/scope.js
index 5ebdb7410..7ee1e9f28 100644
--- a/modules/domQueries/scope.js
+++ b/modules/domQueries/scope.js
@@ -58,7 +58,7 @@
     var context = phantomas.getDOMPath(this);
 
     // querying by BODY and body is the same (issue #419)
-    tagName = tagName.toLowerCase();
+    if (tagName) tagName = tagName.toLowerCase();
 
     phantomas.incrMetric("DOMqueriesByTagName");
     phantomas.addOffender("DOMqueriesByTagName", {
diff --git a/test/webroot/js-errors.html b/test/webroot/js-errors.html
index fc92bf1d3..d253e8626 100644
--- a/test/webroot/js-errors.html
+++ b/test/webroot/js-errors.html
@@ -9,4 +9,11 @@
         // and this one too, but the execution will never reach this linen
         window.Foo('test');
 	</script>
+	<script>
+        // thoses ones should not fail (as in a real browser)
+        document.getElementsByTagName(undefined);
+        document.getElementById(undefined);
+        document.getElementsByClassName(undefined);
+        document.querySelector(undefined);
+	</script>
 </body>