diff --git a/kernel.rb b/kernel.rb
index 888ef0c531..5d596c8892 100644
--- a/kernel.rb
+++ b/kernel.rb
@@ -17,7 +17,7 @@ module Kernel
   #
   def class
     Primitive.attr! :leaf
-    Primitive.cexpr! 'rb_obj_class(self)'
+    Primitive.cexpr! 'rb_obj_class_must(self)'
   end
 
   #
diff --git a/object.c b/object.c
index dc5ab2d934..1ac14ec634 100644
--- a/object.c
+++ b/object.c
@@ -281,6 +281,7 @@ rb_obj_not_equal(VALUE obj1, VALUE obj2)
 static inline VALUE
 fake_class_p(VALUE klass)
 {
+    RUBY_ASSERT(klass);
     RUBY_ASSERT(RB_TYPE_P(klass, T_CLASS) || RB_TYPE_P(klass, T_MODULE) || RB_TYPE_P(klass, T_ICLASS));
     STATIC_ASSERT(t_iclass_overlap_t_class, !(T_CLASS & T_ICLASS));
     STATIC_ASSERT(t_iclass_overlap_t_module, !(T_MODULE & T_ICLASS));
@@ -307,6 +308,17 @@ rb_obj_class(VALUE obj)
     return cl;
 }
 
+VALUE
+rb_obj_class_must(VALUE obj)
+{
+    VALUE cl = CLASS_OF(obj);
+    RUBY_ASSERT(cl);
+    while (RB_UNLIKELY(fake_class_p(cl))) {
+        cl = RCLASS_SUPER(cl);
+    }
+    return cl;
+}
+
 /*
  *  call-seq:
  *     obj.singleton_class    -> class