diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index f2a7532883c..407ff4694e4 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -70,6 +70,16 @@ pub struct GeckoDeclarationBlock {
     pub immutable: AtomicBool,
 }
 
+impl PartialEq for GeckoDeclarationBlock {
+    fn eq(&self, other: &GeckoDeclarationBlock) -> bool {
+        match (&self.declarations, &other.declarations) {
+            (&None, &None) => true,
+            (&Some(ref s), &Some(ref other)) => *s.read() == *other.read(),
+            _ => false,
+        }
+    }
+}
+
 unsafe impl HasFFI for GeckoDeclarationBlock {
     type FFIType = bindings::ServoDeclarationBlock;
 }
diff --git a/components/style/gecko_bindings/bindings.rs b/components/style/gecko_bindings/bindings.rs
index 46131cf6908..92675468073 100644
--- a/components/style/gecko_bindings/bindings.rs
+++ b/components/style/gecko_bindings/bindings.rs
@@ -872,6 +872,11 @@ extern "C" {
     pub fn Servo_DeclarationBlock_Release(declarations:
                                               ServoDeclarationBlockBorrowed);
 }
+extern "C" {
+    pub fn Servo_DeclarationBlock_Equals(a: ServoDeclarationBlockBorrowed,
+                                         b: ServoDeclarationBlockBorrowed)
+     -> bool;
+}
 extern "C" {
     pub fn Servo_DeclarationBlock_GetCache(declarations:
                                                ServoDeclarationBlockBorrowed)
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 33a78d874b2..499c9c9d4e1 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -413,6 +413,13 @@ pub extern "C" fn Servo_DeclarationBlock_Release(declarations: ServoDeclarationB
     unsafe { GeckoDeclarationBlock::release(declarations) };
 }
 
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_Equals(a: ServoDeclarationBlockBorrowed,
+                                                b: ServoDeclarationBlockBorrowed)
+                                                -> bool {
+    GeckoDeclarationBlock::as_arc(&a) == GeckoDeclarationBlock::as_arc(&b)
+}
+
 #[no_mangle]
 pub extern "C" fn Servo_DeclarationBlock_GetCache(declarations: ServoDeclarationBlockBorrowed)
                                                  -> *mut nsHTMLCSSStyleSheet {