diff --git a/storage/innobase/sync/sync0sync.cc b/storage/innobase/sync/sync0sync.cc
index 2928fb0598b..7225ac1a0dc 100644
--- a/storage/innobase/sync/sync0sync.cc
+++ b/storage/innobase/sync/sync0sync.cc
@@ -47,14 +47,20 @@ Created 9/5/1995 Heikki Tuuri
 #include "ha_prototypes.h"
 #include "my_cpu.h"
 
-/* There is a bug in Visual Studio 2010
+/* There is a bug in Visual Studio 2010.
 Visual Studio has a feature "Checked Iterators". In a debug build, every
-iterator operation is checked at runtime for errors, e g, out of range.
+iterator operation is checked at runtime for errors, e.g., out of range.
+Because of bug there is runtime error on following code
+for (std::vector<sync_level_t>::iterator it = array->elems.begin(); it !=
+array->elems.end(); ++it) and runtime check fails on comparison
+it != array->elems.end() that is correct and standard way to do end
+of range comparison.
 Disable this "Checked Iterators" for Windows and Debug if defined.
 */
 #ifdef UNIV_DEBUG
 #ifdef __WIN__
 #ifdef _ITERATOR_DEBUG_LEVEL
+#undef  _ITERATOR_DEBUG_LEVEL
 #define _ITERATOR_DEBUG_LEVEL 0
 #endif /* _ITERATOR_DEBUG_LEVEL */
 #endif /* __WIN__*/
diff --git a/storage/xtradb/sync/sync0sync.cc b/storage/xtradb/sync/sync0sync.cc
index b8766699413..131aa718dc9 100644
--- a/storage/xtradb/sync/sync0sync.cc
+++ b/storage/xtradb/sync/sync0sync.cc
@@ -48,14 +48,20 @@ Created 9/5/1995 Heikki Tuuri
 #include "ha_prototypes.h"
 #include "my_cpu.h"
 
-/* There is a bug in Visual Studio 2010
+/* There is a bug in Visual Studio 2010.
 Visual Studio has a feature "Checked Iterators". In a debug build, every
-iterator operation is checked at runtime for errors, e g, out of range.
+iterator operation is checked at runtime for errors, e.g., out of range.
+Because of bug there is runtime error on following code
+for (std::vector<sync_level_t>::iterator it = array->elems.begin(); it !=
+array->elems.end(); ++it) and runtime check fails on comparison
+it != array->elems.end() that is correct and standard way to do end
+of range comparison.
 Disable this "Checked Iterators" for Windows and Debug if defined.
 */
 #ifdef UNIV_DEBUG
 #ifdef __WIN__
 #ifdef _ITERATOR_DEBUG_LEVEL
+#undef  _ITERATOR_DEBUG_LEVEL
 #define _ITERATOR_DEBUG_LEVEL 0
 #endif /* _ITERATOR_DEBUG_LEVEL */
 #endif /* __WIN__*/