diff --git a/components/script/dom/cssstyledeclaration.rs b/components/script/dom/cssstyledeclaration.rs
index 161c0d16b9f..3cba121d13a 100644
--- a/components/script/dom/cssstyledeclaration.rs
+++ b/components/script/dom/cssstyledeclaration.rs
@@ -16,7 +16,7 @@ use dom::window::{Window, WindowHelpers};
 use util::str::DOMString;
 use selectors::parser::PseudoElement;
 use string_cache::Atom;
-use style::properties::{is_supported_property, longhands_from_shorthand, parse_style_attribute};
+use style::properties::{is_supported_property, longhands_from_shorthand, parse_one_declaration};
 use style::properties::PropertyDeclaration;
 
 use std::ascii::AsciiExt;
@@ -228,37 +228,31 @@ impl<'a> CSSStyleDeclarationMethods for &'a CSSStyleDeclaration {
         }
 
         // Step 5
-        let priority = priority.to_ascii_lowercase();
-        if priority != "!important" && !priority.is_empty() {
-            return Ok(());
-        }
+        let priority = match &*priority {
+            "" => StylePriority::Normal,
+            p if p.eq_ignore_ascii_case("important") => StylePriority::Important,
+            _ => return Ok(()),
+        };
 
         // Step 6
-        let mut synthesized_declaration = property;
-        synthesized_declaration.push_str(": ");
-        synthesized_declaration.push_str(&value);
-
         let owner = self.owner.root();
         let window = window_from_node(owner.r());
-        let decl_block = parse_style_attribute(&synthesized_declaration, &window.r().get_url());
+        let declarations = parse_one_declaration(&property, &value, &window.r().get_url());
 
         // Step 7
-        if decl_block.normal.len() == 0 {
+        let declarations = if let Ok(declarations) = declarations {
+            declarations
+        } else {
             return Ok(());
-        }
+        };
 
         let owner = self.owner.root();
         let element = ElementCast::from_ref(owner.r());
 
         // Step 8
-        for decl in decl_block.normal.iter() {
+        for decl in declarations {
             // Step 9
-            let style_priority = if priority.is_empty() {
-                StylePriority::Normal
-            } else {
-                StylePriority::Important
-            };
-            element.update_inline_style(decl.clone(), style_priority);
+            element.update_inline_style(decl, priority);
         }
 
         let document = document_from_node(element);
diff --git a/components/script/dom/element.rs b/components/script/dom/element.rs
index 03edf9a35e6..9ce21324c6f 100644
--- a/components/script/dom/element.rs
+++ b/components/script/dom/element.rs
@@ -564,7 +564,7 @@ impl LayoutElementHelpers for LayoutJS<Element> {
     }
 }
 
-#[derive(PartialEq)]
+#[derive(PartialEq, Eq, Copy, Clone)]
 pub enum StylePriority {
     Important,
     Normal,
diff --git a/components/style/properties.mako.rs b/components/style/properties.mako.rs
index e6531e41687..9fa9819ab9f 100644
--- a/components/style/properties.mako.rs
+++ b/components/style/properties.mako.rs
@@ -5534,6 +5534,15 @@ pub fn parse_style_attribute(input: &str, base_url: &Url) -> PropertyDeclaration
     parse_property_declaration_list(&context, &mut Parser::new(input))
 }
 
+pub fn parse_one_declaration(name: &str, input: &str, base_url: &Url)
+                             -> Result<Vec<PropertyDeclaration>, ()> {
+    let context = ParserContext::new(Origin::Author, base_url);
+    let mut results = vec![];
+    match PropertyDeclaration::parse(name, &context, &mut Parser::new(input), &mut results) {
+        PropertyDeclarationParseResult::ValidOrIgnoredDeclaration => Ok(results),
+        _ => Err(())
+    }
+}
 
 struct PropertyDeclarationParser<'a, 'b: 'a> {
     context: &'a ParserContext<'b>,