diff --git a/core/src/display_object/movie_clip.rs b/core/src/display_object/movie_clip.rs
index 68066c412..df5a13a13 100644
--- a/core/src/display_object/movie_clip.rs
+++ b/core/src/display_object/movie_clip.rs
@@ -397,7 +397,7 @@ impl<'gc> MovieClip<'gc> {
             TagCode::DefineButtonCxform => self
                 .0
                 .write(context.gc_context)
-                .define_button_cxform(context, reader, tag_len),
+                .define_button_cxform(context, reader),
             TagCode::DefineButtonSound => self
                 .0
                 .write(context.gc_context)
@@ -2998,9 +2998,8 @@ impl<'gc, 'a> MovieClipData<'gc> {
         &mut self,
         context: &mut UpdateContext<'_, 'gc, '_>,
         reader: &mut SwfStream<'a>,
-        tag_len: usize,
     ) -> DecodeResult {
-        let button_colors = reader.read_define_button_cxform(tag_len)?;
+        let button_colors = reader.read_define_button_cxform()?;
         match context
             .library
             .library_for_movie_mut(self.movie())
diff --git a/swf/src/read.rs b/swf/src/read.rs
index eaac38e5a..6f6460044 100644
--- a/swf/src/read.rs
+++ b/swf/src/read.rs
@@ -390,7 +390,7 @@ impl<'a> Reader<'a> {
                 Tag::DefineButton2(Box::new(tag_reader.read_define_button_2()?))
             }
             TagCode::DefineButtonCxform => {
-                Tag::DefineButtonColorTransform(tag_reader.read_define_button_cxform(length)?)
+                Tag::DefineButtonColorTransform(tag_reader.read_define_button_cxform()?)
             }
             TagCode::DefineButtonSound => {
                 Tag::DefineButtonSound(Box::new(tag_reader.read_define_button_sound()?))
@@ -790,18 +790,15 @@ impl<'a> Reader<'a> {
         })
     }
 
-    pub fn read_define_button_cxform(&mut self, tag_length: usize) -> Result<ButtonColorTransform> {
+    pub fn read_define_button_cxform(&mut self) -> Result<ButtonColorTransform> {
         // SWF19 is incorrect here. You can have >1 color transforms in this tag. They apply
         // to the characters in a button in sequence.
 
-        // We don't know how many color transforms this tag will contain, so read it into a buffer.
-        let mut reader = Reader::new(self.read_slice(tag_length)?, self.version);
-
-        let id = reader.read_character_id()?;
+        let id = self.read_character_id()?;
         let mut color_transforms = Vec::new();
 
         // Read all color transforms.
-        while let Ok(color_transform) = reader.read_color_transform_no_alpha() {
+        while let Ok(color_transform) = self.read_color_transform_no_alpha() {
             color_transforms.push(color_transform);
         }