diff --git a/src/components/script/dom/bindings/str.rs b/src/components/script/dom/bindings/str.rs
index a091060c66b..ae6c721abea 100644
--- a/src/components/script/dom/bindings/str.rs
+++ b/src/components/script/dom/bindings/str.rs
@@ -47,6 +47,9 @@ impl ByteString {
 
     pub fn is_token(&self) -> bool {
         let ByteString(ref vec) = *self;
+        if vec.len() == 0 {
+            return false; // A token must be at least a single character
+        }
         vec.iter().all(|&x| {
             // http://tools.ietf.org/html/rfc2616#section-2.2
             match x {
@@ -55,6 +58,7 @@ impl ByteString {
                 44 | 59 | 58 | 92 | 34 |
                 47 | 91 | 93 | 63 | 61 |
                 123 | 125 | 32  => false, // separators
+                x if x > 127 => false, // non-CHARs
                 _ => true
             }
         })
diff --git a/src/components/script/dom/xmlhttprequest.rs b/src/components/script/dom/xmlhttprequest.rs
index 60af7c394b1..cc99bb4ea88 100644
--- a/src/components/script/dom/xmlhttprequest.rs
+++ b/src/components/script/dom/xmlhttprequest.rs
@@ -301,7 +301,7 @@ impl<'a> XMLHttpRequestMethods<'a> for JSRef<'a, XMLHttpRequest> {
                 };
                 // XXXManishearth Do some handling of username/passwords
                 if self.sync {
-                    // FIXME: This should only happen if the global environmet is a document environment
+                    // FIXME: This should only happen if the global environment is a document environment
                     if self.timeout != 0 || self.with_credentials || self.response_type != _empty {
                         return Err(InvalidAccess)
                     }
@@ -320,6 +320,8 @@ impl<'a> XMLHttpRequestMethods<'a> for JSRef<'a, XMLHttpRequest> {
                 }
                 Ok(())
             },
+            // This includes cases where as_str() returns None, and when is_token() returns false,
+            // both of which indicate invalid extension method names
             _ => Err(Syntax), // Step 3
         }
     }