diff --git a/sdk/lib/cmlib/hivedata.h b/sdk/lib/cmlib/hivedata.h
index 16f96de6b4f..648176a0dc6 100644
--- a/sdk/lib/cmlib/hivedata.h
+++ b/sdk/lib/cmlib/hivedata.h
@@ -33,7 +33,8 @@
 #define HFILE_TYPE_PRIMARY              0
 #define HFILE_TYPE_LOG                  1
 #define HFILE_TYPE_EXTERNAL             2
-#define HFILE_TYPE_MAX                  3
+#define HFILE_TYPE_ALTERNATE            3 // Technically a HFILE_TYPE_PRIMARY but for mirror backup hives. ONLY USED for the SYSTEM hive!
+#define HFILE_TYPE_MAX                  4
 
 //
 // Hive sizes
diff --git a/sdk/lib/cmlib/hivewrt.c b/sdk/lib/cmlib/hivewrt.c
index 4fea5fa70e6..2e8d34d1905 100644
--- a/sdk/lib/cmlib/hivewrt.c
+++ b/sdk/lib/cmlib/hivewrt.c
@@ -135,7 +135,7 @@ HvpWriteLog(
      * Now calculate the bitmap and buffer sizes to hold up our
      * contents in a buffer.
      */
-    BitmapSize = ROUND_UP(sizeof(ULONG) + RegistryHive->DirtyVector.SizeOfBitMap / 8, HSECTOR_SIZE);
+    BitmapSize = ROUND_UP(sizeof(ULONG) + RegistryHive->DirtyVector.SizeOfBitMap, HSECTOR_SIZE);
     BufferSize = HV_LOG_HEADER_SIZE + BitmapSize;
 
     /* Now allocate the base header block buffer */