diff --git a/src/internals.h b/src/internals.h
index a3ba11b1..dbe7aeac 100644
--- a/src/internals.h
+++ b/src/internals.h
@@ -67,7 +67,7 @@
 #endif
 #ifndef _CRT_SECURE_NO_WARNINGS
 #define _CRT_SECURE_NO_WARNINGS
-#endif
+#endif /* _CRT_SECURE_NO_WARNINGS */
 #if _MSC_VER > 1800
 #pragma warning(disable : 4464) /* relative include path contains '..' */
 #endif
diff --git a/src/mdbx.c++ b/src/mdbx.c++
index 82770c69..a6db48ff 100644
--- a/src/mdbx.c++
+++ b/src/mdbx.c++
@@ -5,9 +5,9 @@
 // Non-inline part of the libmdbx C++ API (preliminary)
 //
 
-#ifdef _MSC_VER
+#if defined(_MSC_VER) && !defined(_CRT_SECURE_NO_WARNINGS)
 #define _CRT_SECURE_NO_WARNINGS
-#endif
+#endif /* _CRT_SECURE_NO_WARNINGS */
 
 #include "../mdbx.h++"
 
diff --git a/src/osal.h b/src/osal.h
index 478b7328..2e8359b5 100644
--- a/src/osal.h
+++ b/src/osal.h
@@ -33,7 +33,7 @@
 #if defined(_WIN32) || defined(_WIN64)
 #if !defined(_CRT_SECURE_NO_WARNINGS)
 #define _CRT_SECURE_NO_WARNINGS
-#endif
+#endif /* _CRT_SECURE_NO_WARNINGS */
 #if !defined(_NO_CRT_STDIO_INLINE) && MDBX_BUILD_SHARED_LIBRARY &&             \
     !defined(xMDBX_TOOLS) && MDBX_WITHOUT_MSVC_CRT
 #define _NO_CRT_STDIO_INLINE
diff --git a/test/base.h b/test/base.h
index 790ffd0f..89fd91e0 100644
--- a/test/base.h
+++ b/test/base.h
@@ -23,7 +23,9 @@
 #define _WIN32_WINNT 0x0601 /* Windows 7 */
 #endif
 #ifdef _MSC_VER
+#ifndef _CRT_SECURE_NO_WARNINGS
 #define _CRT_SECURE_NO_WARNINGS
+#endif /* _CRT_SECURE_NO_WARNINGS */
 #pragma warning(push, 1)
 #pragma warning(disable : 4548) /* expression before comma has no effect;      \
                                    expected expression with side - effect */