diff --git a/layout/style/nsCSSScanner.cpp b/layout/style/nsCSSScanner.cpp
index e02b164c3aed..6fe1834b2e16 100644
--- a/layout/style/nsCSSScanner.cpp
+++ b/layout/style/nsCSSScanner.cpp
@@ -936,12 +936,6 @@ nsCSSScanner::NextURL(nsCSSToken& aToken)
     if (ch < 0) break;
     if (ch == CSS_ESCAPE) {
       ParseAndAppendEscape(ident);
-    } else if ((ch == '"') || (ch == '\'') || (ch == '(')) {
-      // This is an invalid URL spec
-      ok = PR_FALSE;
-      Pushback(ch); // push it back so the parser can match tokens and
-                    // then closing parenthesis
-      break;
     } else if (IsWhitespace(ch)) {
       // Whitespace is allowed at the end of the URL
       EatWhiteSpace();
@@ -954,6 +948,12 @@ nsCSSScanner::NextURL(nsCSSToken& aToken)
       // ")". This is an invalid url spec.
       ok = PR_FALSE;
       break;
+    } else if (ch == '"' || ch == '\'' || ch == '(' || ch < PRUnichar(' ')) {
+      // This is an invalid URL spec
+      ok = PR_FALSE;
+      Pushback(ch); // push it back so the parser can match tokens and
+                    // then closing parenthesis
+      break;
     } else if (ch == ')') {
       Pushback(ch);
       // All done
diff --git a/layout/style/test/test_parse_url.html b/layout/style/test/test_parse_url.html
index 259c1cebdb01..011b3080b21d 100644
--- a/layout/style/test/test_parse_url.html
+++ b/layout/style/test/test_parse_url.html
@@ -153,6 +153,16 @@ div.style.listStyleImage = 'url(cc\\f  b)';
 is(div.style.listStyleImage, 'url("bad")',
    "unquoted URL with spaces not allowed");
 
+var chars = [ 1, 2, 3, 4, 5, 6, 7, 8, 11, 14, 15, 16, 17, 18, 19, 20,
+              21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 ];
+
+for (var i in chars) {
+  var charcode = chars[i];
+  div.style.listStyleImage = 'url(' + String.fromCharCode(charcode) + ')';
+  is(div.style.listStyleImage, 'url("bad")',
+     "unquoted URL with control character " + charcode + " not allowed");
+}
+
 div.style.listStyleImage = 'url(\\f good)';
 is(div.style.listStyleImage, 'url("\\F good")', "URL allowed");
 div.style.listStyleImage = 'url( \\f good)';