diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
index 3b0c35b..46e8427 100644
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -1946,14 +1946,17 @@
 
 /* Special bytes broadcast into debug memory blocks at appropriate times.
  * Strings of these are unlikely to be valid addresses, floats, ints or
- * 7-bit ASCII.
+ * 7-bit ASCII. If modified, _PyMem_IsPtrFreed() should be updated as well.
+ *
+ * Byte patterns 0xCB, 0xBB and 0xFB have been replaced with 0xCD, 0xDD and
+ * 0xFD to use the same values than Windows CRT debug malloc() and free().
  */
 #undef CLEANBYTE
 #undef DEADBYTE
 #undef FORBIDDENBYTE
-#define CLEANBYTE      0xCB    /* clean (newly allocated) memory */
-#define DEADBYTE       0xDB    /* dead (newly freed) memory */
-#define FORBIDDENBYTE  0xFB    /* untouchable bytes at each end of a block */
+#define CLEANBYTE      0xCD    /* clean (newly allocated) memory */
+#define DEADBYTE       0xDD    /* dead (newly freed) memory */
+#define FORBIDDENBYTE  0xFD    /* untouchable bytes at each end of a block */
 
 static size_t serialno = 0;     /* incremented on each debug {m,re}alloc */
 
@@ -2091,22 +2094,6 @@
 }
 
 
-/* Heuristic checking if the memory has been freed. Rely on the debug hooks on
-   Python memory allocators which fills the memory with DEADBYTE (0xDB) when
-   memory is deallocated. */
-int
-_PyMem_IsFreed(void *ptr, size_t size)
-{
-    unsigned char *bytes = ptr;
-    for (size_t i=0; i < size; i++) {
-        if (bytes[i] != DEADBYTE) {
-            return 0;
-        }
-    }
-    return 1;
-}
-
-
 /* The debug free first checks the 2*SST bytes on each end for sanity (in
    particular, that the FORBIDDENBYTEs with the api ID are still intact).
    Then fills the original bytes with DEADBYTE.