diff --git a/src/components/script/dom/bindings/utils.rs b/src/components/script/dom/bindings/utils.rs
index 934625a83f4..e37f1d68153 100644
--- a/src/components/script/dom/bindings/utils.rs
+++ b/src/components/script/dom/bindings/utils.rs
@@ -770,6 +770,7 @@ pub enum Error {
     FailureUnknown,
     NotFound,
     HierarchyRequest,
+    InvalidCharacter,
 }
 
 pub type ErrorResult = Result<(), Error>;
@@ -832,3 +833,59 @@ pub fn CreateDOMGlobal(cx: *JSContext, class: *JSClass) -> *JSObject {
         obj
     }
 }
+
+/// Check if an element name is valid. See http://www.w3.org/TR/xml/#NT-Name
+/// for details.
+pub fn is_valid_element_name(name: &str) -> bool {
+    fn is_valid_start(c: char) -> bool {
+        match c {
+            ':' |
+            'A' .. 'Z' |
+            '_' |
+            'a' .. 'z' |
+            '\xC0' .. '\xD6' |
+            '\xD8' .. '\xF6' |
+            '\xF8' .. '\u02FF' |
+            '\u0370' .. '\u037D' |
+            '\u037F' .. '\u1FFF' |
+            '\u200C' .. '\u200D' |
+            '\u2070' .. '\u218F' |
+            '\u2C00' .. '\u2FEF' |
+            '\u3001' .. '\uD7FF' |
+            '\uF900' .. '\uFDCF' |
+            '\uFDF0' .. '\uFFFD' |
+            '\U00010000' .. '\U000EFFFF' => true,
+            _ => false,
+        }
+    }
+
+    fn is_valid_continuation(c: char) -> bool {
+        is_valid_start(c) || match c {
+            '-' |
+            '.' |
+            '0' .. '9' |
+            '\xB7' |
+            '\u0300' .. '\u036F' |
+            '\u203F' .. '\u2040' => true,
+            _ => false,
+        }
+    }
+
+    let mut iter = name.iter();
+    match iter.next() {
+        None => return false,
+        Some(c) => {
+            if !is_valid_start(c) {
+                return false;
+            }
+        }
+    }
+
+    for c in name.iter() {
+        if !is_valid_continuation(c) {
+            return false;
+        }
+    }
+
+    true
+}
diff --git a/src/components/script/dom/document.rs b/src/components/script/dom/document.rs
index 5472c10728b..d84f2427f8d 100644
--- a/src/components/script/dom/document.rs
+++ b/src/components/script/dom/document.rs
@@ -5,7 +5,7 @@
 use dom::bindings::codegen::DocumentBinding;
 use dom::bindings::utils::{DOMString, WrapperCache, ErrorResult, null_string, str};
 use dom::bindings::utils::{BindingObject, CacheableWrapper, rust_box, DerivedWrapper};
-use dom::bindings::utils::Traceable;
+use dom::bindings::utils::{is_valid_element_name, InvalidCharacter, Traceable};
 use dom::element::{Element};
 use dom::element::{HTMLHtmlElementTypeId, HTMLHeadElementTypeId, HTMLTitleElementTypeId};
 use dom::event::Event;
@@ -28,6 +28,7 @@ use std::cast;
 use std::ptr;
 use std::str::eq_slice;
 use std::libc;
+use std::ascii::StrAsciiExt;
 
 pub trait WrappableDocument {
     fn init_wrapper(@mut self, cx: *JSContext);
@@ -240,9 +241,16 @@ impl Document {
         None
     }
 
-    pub fn CreateElement(&self, local_name: &DOMString, _rv: &mut ErrorResult) -> AbstractNode<ScriptView> {
+    pub fn CreateElement(&self, local_name: &DOMString, rv: &mut ErrorResult) -> AbstractNode<ScriptView> {
         let cx = self.get_cx();
-        build_element_from_tag(cx, local_name.to_str())
+        let local_name = local_name.to_str();
+        if !is_valid_element_name(local_name) {
+            *rv = Err(InvalidCharacter);
+            // FIXME #909: what to return here?
+            fail!("invalid character");
+        }
+        let local_name = local_name.to_ascii_lower();
+        build_element_from_tag(cx, local_name)
     }
 
     pub fn CreateElementNS(&self, _namespace: &DOMString, _qualified_name: &DOMString, _rv: &mut ErrorResult) -> AbstractNode<ScriptView> {
diff --git a/src/test/html/content/test_create_element.html b/src/test/html/content/test_create_element.html
index c59106b6603..eaa3e11377a 100644
--- a/src/test/html/content/test_create_element.html
+++ b/src/test/html/content/test_create_element.html
@@ -9,6 +9,8 @@
     is(elem.tagName, "FOO");
     var elem = document.createElement("p");
     is(elem instanceof HTMLParagraphElement, true);
+    var elem = document.createElement("sPAn");
+    is(elem instanceof HTMLSpanElement, true);
     var text = document.createTextNode("hello");
     is(text instanceof Text, true);
     finish();