diff --git a/ext/msgpack/unpacker.c b/ext/msgpack/unpacker.c
index 2178c9b1..7ee9463f 100644
--- a/ext/msgpack/unpacker.c
+++ b/ext/msgpack/unpacker.c
@@ -95,7 +95,8 @@ void msgpack_unpacker_static_destroy(void)
     msgpack_rmem_destroy(&s_stack_rmem);
 }
 
-#define HEAD_BYTE_REQUIRED 0xc1
+/* outside 0..255 so it never collides with a real byte, including the invalid 0xc1 */
+#define HEAD_BYTE_REQUIRED 0x100
 
 static inline bool _msgpack_unpacker_stack_init(msgpack_unpacker_stack_t *stack) {
     if (!stack->data) {
diff --git a/spec/cruby/unpacker_spec.rb b/spec/cruby/unpacker_spec.rb
index ae8c9b22..068e1c07 100644
--- a/spec/cruby/unpacker_spec.rb
+++ b/spec/cruby/unpacker_spec.rb
@@ -67,5 +67,33 @@
       unpacker.skip
     }.should raise_error(MessagePack::MalformedFormatError)
   end
+
+  it 'skip_nil keeps invalid byte' do
+    unpacker.feed("\xc1\x01")
+    unpacker.skip_nil.should == false
+    lambda {
+      unpacker.read
+    }.should raise_error(MessagePack::MalformedFormatError)
+  end
+
+  it 'read_array_header keeps invalid byte' do
+    unpacker.feed("\xc1\x01")
+    lambda {
+      unpacker.read_array_header
+    }.should raise_error(MessagePack::UnpackError)
+    lambda {
+      unpacker.read
+    }.should raise_error(MessagePack::MalformedFormatError)
+  end
+
+  it 'read_map_header keeps invalid byte' do
+    unpacker.feed("\xc1\x01")
+    lambda {
+      unpacker.read_map_header
+    }.should raise_error(MessagePack::UnpackError)
+    lambda {
+      unpacker.read
+    }.should raise_error(MessagePack::MalformedFormatError)
+  end
 end