diff --git a/components/script/dom/cssstyledeclaration.rs b/components/script/dom/cssstyledeclaration.rs
index f11cabd7989..d347b63b3b0 100644
--- a/components/script/dom/cssstyledeclaration.rs
+++ b/components/script/dom/cssstyledeclaration.rs
@@ -126,34 +126,20 @@ impl CSSStyleDeclarationMethods for CSSStyleDeclaration {
 
     // https://dev.w3.org/csswg/cssom/#dom-cssstyledeclaration-getpropertypriority
     fn GetPropertyPriority(&self, mut property: DOMString) -> DOMString {
-        // Step 1
-        property.make_ascii_lowercase();
-        let property = Atom::from(property);
-
-        // Step 2
-        if let Some(shorthand) = Shorthand::from_name(&property) {
-            // Step 2.1 & 2.2 & 2.3
-            if shorthand.longhands().iter()
-                                    .map(|&longhand| self.GetPropertyPriority(DOMString::from(longhand)))
-                                    .all(|priority| priority == "important") {
-                return DOMString::from("important");
-            }
+        let style_attribute = self.owner.style_attribute().borrow();
+        let style_attribute = if let Some(ref style_attribute) = *style_attribute {
+            style_attribute.read()
         } else {
-            // Step 3
-            return self.owner.get_inline_style_declaration(&property, |d| {
-                if let Some(decl) = d {
-                    if decl.1.important() {
-                        return DOMString::from("important");
-                    }
-                }
+            // No style attribute is like an empty style attribute: no matching declaration.
+            return DOMString::new()
+        };
 
-                // Step 4
-                DOMString::new()
-            })
+        if style_attribute.property_priority(&property).important() {
+            DOMString::from("important")
+        } else {
+            // Step 4
+            DOMString::new()
         }
-
-        // Step 4
-        DOMString::new()
     }
 
     // https://dev.w3.org/csswg/cssom/#dom-cssstyledeclaration-setproperty
diff --git a/components/script/dom/element.rs b/components/script/dom/element.rs
index 13937bf904c..4c2ac626e7e 100644
--- a/components/script/dom/element.rs
+++ b/components/script/dom/element.rs
@@ -872,17 +872,6 @@ impl Element {
         self.sync_property_with_attrs_style();
     }
 
-    pub fn get_inline_style_declaration<F, R>(&self, property: &str, f: F) -> R
-    where F: FnOnce(Option<&(PropertyDeclaration, Importance)>) -> R {
-        let style_attr = self.style_attribute.borrow();
-        if let Some(ref block) = *style_attr {
-            let block = block.read();
-            f(block.get(property))
-        } else {
-            f(None)
-        }
-    }
-
     pub fn serialize(&self, traversal_scope: TraversalScope) -> Fallible<DOMString> {
         let mut writer = vec![];
         match serialize(&mut writer,
diff --git a/components/style/properties/declaration_block.rs b/components/style/properties/declaration_block.rs
index 44af1a75ef0..10f4eb42d84 100644
--- a/components/style/properties/declaration_block.rs
+++ b/components/style/properties/declaration_block.rs
@@ -109,6 +109,27 @@ impl PropertyDeclarationBlock {
         }
     }
 
+    /// https://dev.w3.org/csswg/cssom/#dom-cssstyledeclaration-getpropertypriority
+    pub fn property_priority(&self, property_name: &str) -> Importance {
+        // Step 1
+        let property = property_name.to_ascii_lowercase();
+
+        // Step 2
+        if let Some(shorthand) = Shorthand::from_name(&property) {
+            // Step 2.1 & 2.2 & 2.3
+            if shorthand.longhands().iter().all(|l| {
+                self.get(l).map_or(false, |&(_, importance)| importance.important())
+            }) {
+                Importance::Important
+            } else {
+                Importance::Normal
+            }
+        } else {
+            // Step 3
+            self.get(&property).map_or(Importance::Normal, |&(_, importance)| importance)
+        }
+    }
+
     /// Take a declaration block known to contain a single property and serialize it.
     pub fn single_value_to_css<W>(&self, property_name: &str, dest: &mut W) -> fmt::Result
     where W: fmt::Write {