diff --git a/data_provider.rs b/data_provider.rs
index ee94628..01e3044 100644
--- a/data_provider.rs
+++ b/data_provider.rs
@@ -32,7 +32,7 @@ impl AbstractCFTypeRef for CGDataProviderRef {
     fn as_type_ref(&self) -> CFTypeRef { *self as CFTypeRef }
 
     #[fixed_stack_segment]
-    fn type_id() -> CFTypeID {
+    fn type_id(_dummy: Option<CGDataProviderRef>) -> CFTypeID {
         unsafe {
             CGDataProviderGetTypeID()
         }
diff --git a/font.rs b/font.rs
index 2bc7bf5..d826d0c 100644
--- a/font.rs
+++ b/font.rs
@@ -21,7 +21,7 @@ impl AbstractCFTypeRef for CGFontRef {
     fn as_type_ref(&self) -> CFTypeRef { *self as CFTypeRef }
 
     #[fixed_stack_segment]
-    fn type_id() -> CFTypeID {
+    fn type_id(_dummy: Option<CGFontRef>) -> CFTypeID {
         unsafe {
             CGFontGetTypeID()
         }