diff --git a/font.rs b/font.rs
index 9135517..e02420b 100644
--- a/font.rs
+++ b/font.rs
@@ -78,7 +78,7 @@ impl AbstractCFTypeRef for CTFontRef {
     fn as_type_ref(&self) -> CFTypeRef { *self as CFTypeRef }
 
     #[fixed_stack_segment]
-    fn type_id() -> CFTypeID {
+    fn type_id(_dummy: Option<CTFontRef>) -> CFTypeID {
         unsafe {
             CTFontGetTypeID()
         }
diff --git a/font_collection.rs b/font_collection.rs
index 25f437c..d011bdc 100644
--- a/font_collection.rs
+++ b/font_collection.rs
@@ -27,7 +27,7 @@ impl AbstractCFTypeRef for CTFontCollectionRef {
     fn as_type_ref(&self) -> CFTypeRef { *self as CFTypeRef }
 
     #[fixed_stack_segment]
-    fn type_id() -> CFTypeID {
+    fn type_id(_dummy: Option<CTFontCollectionRef>) -> CFTypeID {
         unsafe {
             CTFontCollectionGetTypeID()
         }
diff --git a/font_descriptor.rs b/font_descriptor.rs
index f155422..fec5560 100644
--- a/font_descriptor.rs
+++ b/font_descriptor.rs
@@ -188,7 +188,7 @@ impl AbstractCFTypeRef for CTFontDescriptorRef {
     fn as_type_ref(&self) -> CFTypeRef { *self as CFTypeRef }
 
     #[fixed_stack_segment]
-    fn type_id() -> CFTypeID {
+    fn type_id(_dummy: Option<CTFontDescriptorRef>) -> CFTypeID {
         unsafe {
             CTFontDescriptorGetTypeID()
         }