diff --git a/ext/opencv/facerecognizer.cpp b/ext/opencv/facerecognizer.cpp
index d52a448..883b015 100644
--- a/ext/opencv/facerecognizer.cpp
+++ b/ext/opencv/facerecognizer.cpp
@@ -18,20 +18,19 @@ __NAMESPACE_BEGIN_FACERECOGNIZER
 
 VALUE rb_klass;
 
-std::map< long, cv::Ptr<cv::FaceRecognizer> > ptr_guard_map;
+std::map<void*, cv::Ptr<cv::FaceRecognizer> > ptr_guard_map;
 
 void
 guard_facerecognizer(void* data_ptr, cv::Ptr<cv::FaceRecognizer> ptr)
 {
-  ptr_guard_map[(long)data_ptr] = ptr;
+  ptr_guard_map[data_ptr] = ptr;
 }
 
 void
-release_facerecognizer(void *ptr)
+release_facerecognizer(void *data_ptr)
 {
-  long key = (long)ptr;
-  ptr_guard_map[key].release();
-  ptr_guard_map.erase(key);
+  ptr_guard_map[data_ptr].release();
+  ptr_guard_map.erase(data_ptr);
 }
 
 VALUE
diff --git a/ext/opencv/facerecognizer.h b/ext/opencv/facerecognizer.h
index e662b9b..7ea403a 100644
--- a/ext/opencv/facerecognizer.h
+++ b/ext/opencv/facerecognizer.h
@@ -27,7 +27,7 @@ VALUE rb_save(VALUE self, VALUE filename);
 VALUE rb_load(VALUE self, VALUE filename);
 
 void guard_facerecognizer(void* data_ptr, cv::Ptr<cv::FaceRecognizer> ptr);
-void release_facerecognizer(void *ptr);
+void release_facerecognizer(void *data_ptr);
 VALUE allocate_facerecognizer(VALUE klass);
 
 __NAMESPACE_END_FACERECOGNIZER