diff --git a/components/style/cbindgen.toml b/components/style/cbindgen.toml
index 0d2af9f21e7..b5d374d77bf 100644
--- a/components/style/cbindgen.toml
+++ b/components/style/cbindgen.toml
@@ -106,6 +106,7 @@ include = [
   "Contain",
   "RestyleHint",
   "TouchAction",
+  "WillChangeBits",
   "TextDecorationLine",
 ]
 item_types = ["enums", "structs", "typedefs"]
diff --git a/components/style/macros.rs b/components/style/macros.rs
index 6347e5fa4a0..fb189837181 100644
--- a/components/style/macros.rs
+++ b/components/style/macros.rs
@@ -102,20 +102,3 @@ macro_rules! define_keyword_type {
         }
     };
 }
-
-#[cfg(feature = "gecko")]
-macro_rules! impl_bitflags_conversions {
-    ($name:ident) => {
-        impl From<u8> for $name {
-            fn from(bits: u8) -> $name {
-                $name::from_bits(bits).expect("bits contain valid flag")
-            }
-        }
-
-        impl From<$name> for u8 {
-            fn from(v: $name) -> u8 {
-                v.bits()
-            }
-        }
-    };
-}
diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index 82c8e96ec2d..331ffb5c34f 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -2940,10 +2940,10 @@ fn static_assert() {
 
     pub fn set_will_change(&mut self, v: longhands::will_change::computed_value::T) {
         use crate::gecko_bindings::bindings::{Gecko_AppendWillChange, Gecko_ClearWillChange};
-        use crate::properties::longhands::will_change::computed_value::T;
+        use crate::values::specified::box_::{WillChangeBits, WillChange};
 
         match v {
-            T::AnimateableFeatures { features, bits } => {
+            WillChange::AnimateableFeatures { features, bits } => {
                 unsafe {
                     Gecko_ClearWillChange(&mut self.gecko, features.len());
                 }
@@ -2954,13 +2954,13 @@ fn static_assert() {
                     }
                 }
 
-                self.gecko.mWillChangeBitField = bits.bits();
+                self.gecko.mWillChangeBitField = bits;
             },
-            T::Auto => {
+            WillChange::Auto => {
                 unsafe {
                     Gecko_ClearWillChange(&mut self.gecko, 0);
                 }
-                self.gecko.mWillChangeBitField = 0;
+                self.gecko.mWillChangeBitField = WillChangeBits::empty();
             },
         };
     }
@@ -2970,7 +2970,7 @@ fn static_assert() {
 
         self.gecko.mWillChangeBitField = other.gecko.mWillChangeBitField;
         unsafe {
-            Gecko_CopyWillChangeFrom(&mut self.gecko, &other.gecko as *const _ as *mut _);
+            Gecko_CopyWillChangeFrom(&mut self.gecko, &other.gecko);
         }
     }
 
@@ -2979,24 +2979,22 @@ fn static_assert() {
     }
 
     pub fn clone_will_change(&self) -> longhands::will_change::computed_value::T {
-        use crate::properties::longhands::will_change::computed_value::T;
-        use crate::gecko_bindings::structs::nsAtom;
         use crate::values::CustomIdent;
-        use crate::values::specified::box_::WillChangeBits;
+        use crate::values::specified::box_::WillChange;
 
         if self.gecko.mWillChange.len() == 0 {
-            return T::Auto
+            return WillChange::Auto
         }
 
         let custom_idents: Vec<CustomIdent> = self.gecko.mWillChange.iter().map(|gecko_atom| {
             unsafe {
-                CustomIdent(Atom::from_raw(gecko_atom.mRawPtr as *mut nsAtom))
+                CustomIdent(Atom::from_raw(gecko_atom.mRawPtr))
             }
         }).collect();
 
-        T::AnimateableFeatures {
+        WillChange::AnimateableFeatures {
             features: custom_idents.into_boxed_slice(),
-            bits: WillChangeBits::from_bits_truncate(self.gecko.mWillChangeBitField),
+            bits: self.gecko.mWillChangeBitField,
         }
     }
 
diff --git a/components/style/values/specified/box.rs b/components/style/values/specified/box.rs
index dddf3f9b4af..ab81d4c3450 100644
--- a/components/style/values/specified/box.rs
+++ b/components/style/values/specified/box.rs
@@ -555,9 +555,8 @@ impl WillChange {
 
 bitflags! {
     /// The change bits that we care about.
-    ///
-    /// These need to be in sync with NS_STYLE_WILL_CHANGE_*.
     #[derive(MallocSizeOf, SpecifiedValueInfo, ToComputedValue)]
+    #[repr(C)]
     pub struct WillChangeBits: u8 {
         /// Whether the stacking context will change.
         const STACKING_CONTEXT = 1 << 0;
@@ -616,7 +615,7 @@ impl Parse for WillChange {
     fn parse<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
-    ) -> Result<WillChange, ParseError<'i>> {
+    ) -> Result<Self, ParseError<'i>> {
         if input
             .try(|input| input.expect_ident_matching("auto"))
             .is_ok()