diff --git a/gc.c b/gc.c
index 2641115f90..9c7114e5a7 100644
--- a/gc.c
+++ b/gc.c
@@ -626,7 +626,7 @@ typedef struct gc_function_map {
     // Finalizers
     void (*make_zombie)(void *objspace_ptr, VALUE obj, void (*dfree)(void *), void *data);
     VALUE (*define_finalizer)(void *objspace_ptr, VALUE obj, VALUE block);
-    VALUE (*undefine_finalizer)(void *objspace_ptr, VALUE obj);
+    void (*undefine_finalizer)(void *objspace_ptr, VALUE obj);
     void (*copy_finalizer)(void *objspace_ptr, VALUE dest, VALUE obj);
     void (*shutdown_call_finalizer)(void *objspace_ptr);
     // Object ID
@@ -1448,7 +1448,9 @@ os_each_obj(int argc, VALUE *argv, VALUE os)
 static VALUE
 undefine_final(VALUE os, VALUE obj)
 {
-    return rb_gc_impl_undefine_finalizer(rb_gc_get_objspace(), obj);
+    rb_gc_impl_undefine_finalizer(rb_gc_get_objspace(), obj);
+
+    return obj;
 }
 
 static void
diff --git a/gc/default.c b/gc/default.c
index 59890d03be..e5662fc586 100644
--- a/gc/default.c
+++ b/gc/default.c
@@ -3001,7 +3001,7 @@ rb_gc_impl_define_finalizer(void *objspace_ptr, VALUE obj, VALUE block)
     return block;
 }
 
-VALUE
+void
 rb_gc_impl_undefine_finalizer(void *objspace_ptr, VALUE obj)
 {
     rb_objspace_t *objspace = objspace_ptr;
@@ -3009,7 +3009,6 @@ rb_gc_impl_undefine_finalizer(void *objspace_ptr, VALUE obj)
     rb_check_frozen(obj);
     st_delete(finalizer_table, &data, 0);
     FL_UNSET(obj, FL_FINALIZE);
-    return obj;
 }
 
 VALUE
diff --git a/gc/gc_impl.h b/gc/gc_impl.h
index ab21e4e81b..18249dc58b 100644
--- a/gc/gc_impl.h
+++ b/gc/gc_impl.h
@@ -58,7 +58,7 @@ void rb_gc_impl_each_object(void *objspace_ptr, void (*func)(VALUE obj, void *da
 // Finalizers
 void rb_gc_impl_make_zombie(void *objspace_ptr, VALUE obj, void (*dfree)(void *), void *data);
 VALUE rb_gc_impl_define_finalizer(void *objspace_ptr, VALUE obj, VALUE block);
-VALUE rb_gc_impl_undefine_finalizer(void *objspace_ptr, VALUE obj);
+void rb_gc_impl_undefine_finalizer(void *objspace_ptr, VALUE obj);
 void rb_gc_impl_copy_finalizer(void *objspace_ptr, VALUE dest, VALUE obj);
 void rb_gc_impl_shutdown_call_finalizer(void *objspace_ptr);
 // Object ID