diff --git a/spec/core/marshal/dump_spec.rb b/spec/core/marshal/dump_spec.rb
index 5be7b74f3..c2bfdc034 100644
--- a/spec/core/marshal/dump_spec.rb
+++ b/spec/core/marshal/dump_spec.rb
@@ -233,9 +233,7 @@ def _dump(level)
     end
 
     it "raises TypeError with a singleton Class" do
-      NATFIXME 'raises TypeError with a singleton Class', exception: SpecFailedException do
-        -> { Marshal.dump(class << self; self end) }.should raise_error(TypeError)
-      end
+      -> { Marshal.dump(class << self; self end) }.should raise_error(TypeError)
     end
   end
 
diff --git a/src/marshal.rb b/src/marshal.rb
index eb36abdec..badd0995f 100644
--- a/src/marshal.rb
+++ b/src/marshal.rb
@@ -219,6 +219,7 @@ def write_hash(values)
     end
 
     def write_class(value)
+      raise TypeError, "singleton class can't be dumped" if value.singleton_class?
       write_char('c')
       write_string_bytes(value.name)
     end