--- a/servo/components/style/properties/declaration_block.rs
+++ b/servo/components/style/properties/declaration_block.rs
@@ -10,16 +10,17 @@ use cssparser::{DeclarationListParser, p
 use cssparser::{Parser, AtRuleParser, DeclarationParser, Delimiter};
 use error_reporting::ParseErrorReporter;
 use parser::{ParserContext, ParserContextExtraData, log_css_error};
 use servo_url::ServoUrl;
 use std::fmt;
 use style_traits::ToCss;
 use stylesheets::Origin;
 use super::*;
+#[cfg(feature = "gecko")] use properties::animated_properties::AnimationValueMap;
 
 /// A declaration [importance][importance].
 ///
 /// [importance]: https://drafts.csswg.org/css-cascade/#importance
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Importance {
     /// Indicates a declaration without `!important`.
@@ -336,16 +337,34 @@ impl PropertyDeclarationBlock {
                     Some(AppendableValue::DeclarationsForShorthand(_, decls)) => {
                         shorthand.longhands_to_css(decls, dest)
                     }
                     _ => Ok(())
                 }
             }
         }
     }
+
+    /// Convert AnimationValueMap to PropertyDeclarationBlock.
+    #[cfg(feature = "gecko")]
+    pub fn from_animation_value_map(animation_value_map: &AnimationValueMap) -> Self {
+        let mut declarations = vec![];
+        let mut longhands = LonghandIdSet::new();
+
+        for (property, animation_value) in animation_value_map.iter() {
+          longhands.set_transition_property_bit(property);
+          declarations.push((animation_value.uncompute(), Importance::Normal));
+        }
+
+        PropertyDeclarationBlock {
+            declarations: declarations,
+            important_count: 0,
+            longhands: longhands,
+        }
+    }
 }
 
 impl ToCss for PropertyDeclarationBlock {
     // https://drafts.csswg.org/cssom/#serialize-a-css-declaration-block
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result
         where W: fmt::Write,
     {
         let mut is_first_serialization = true; // trailing serializations should have a prepended space