Bug #3951: Py_USING_MEMORY_DEBUGGER should not be enabled by default.
diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
index fc5ccf7..d1586c2 100644
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -677,8 +677,8 @@
 /* This is only useful when running memory debuggers such as
  * Purify or Valgrind.  Uncomment to use.
  *
- */
 #define Py_USING_MEMORY_DEBUGGER
+ */
 
 #ifdef Py_USING_MEMORY_DEBUGGER