diff --git a/components/style/gecko_bindings/bindings.rs b/components/style/gecko_bindings/bindings.rs
index 89089efca0d..16bfaf40fff 100644
--- a/components/style/gecko_bindings/bindings.rs
+++ b/components/style/gecko_bindings/bindings.rs
@@ -750,6 +750,9 @@ extern "C" {
     pub fn Gecko_CSSValue_GetArrayItem(css_value: nsCSSValueBorrowedMut,
                                        index: i32) -> nsCSSValueBorrowedMut;
 }
+extern "C" {
+    pub fn Gecko_CSSValue_Drop(css_value: nsCSSValueBorrowedMut);
+}
 extern "C" {
     pub fn Gecko_AddRefCSSValueSharedListArbitraryThread(aPtr:
                                                              *mut nsCSSValueSharedList);