diff --git a/include/mbedtls/platform.h b/include/mbedtls/platform.h
index 9d9c529..24c6362 100644
--- a/include/mbedtls/platform.h
+++ b/include/mbedtls/platform.h
@@ -55,17 +55,33 @@
  * \{
  */
 
+/* The older Microsoft Windows common runtime provides non-conforming
+ * implementations of some standard library functions, including snprintf
+ * and vsnprintf. This affects MSVC and MinGW builds.
+ */
+#if defined(_MSC_VER) && _MSC_VER <= 1900
+#define MBEDTLS_PLATFORM_HAS_NON_CONFORMING_SNPRINTF
+#define MBEDTLS_PLATFORM_HAS_NON_CONFORMING_VSNPRINTF
+#endif
+
 #if !defined(MBEDTLS_PLATFORM_NO_STD_FUNCTIONS)
 #include <stdio.h>
 #include <stdlib.h>
 #include <time.h>
 #if !defined(MBEDTLS_PLATFORM_STD_SNPRINTF)
-#if defined(_WIN32)
+#if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_SNPRINTF)
 #define MBEDTLS_PLATFORM_STD_SNPRINTF   mbedtls_platform_win32_snprintf /**< The default \c snprintf function to use.  */
 #else
 #define MBEDTLS_PLATFORM_STD_SNPRINTF   snprintf /**< The default \c snprintf function to use.  */
 #endif
 #endif
+#if !defined(MBEDTLS_PLATFORM_STD_VSNPRINTF)
+#if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_VSNPRINTF)
+#define MBEDTLS_PLATFORM_STD_VSNPRINTF   mbedtls_platform_win32_vsnprintf /**< The default \c vsnprintf function to use.  */
+#else
+#define MBEDTLS_PLATFORM_STD_VSNPRINTF   vsnprintf /**< The default \c vsnprintf function to use.  */
+#endif
+#endif
 #if !defined(MBEDTLS_PLATFORM_STD_PRINTF)
 #define MBEDTLS_PLATFORM_STD_PRINTF   printf /**< The default \c printf function to use. */
 #endif
@@ -201,7 +217,7 @@
  * - however it is acceptable to return -1 instead of the required length when
  *   the destination buffer is too short.
  */
-#if defined(_WIN32)
+#if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_SNPRINTF)
 /* For Windows (inc. MSYS2), we provide our own fixed implementation */
 int mbedtls_platform_win32_snprintf( char *s, size_t n, const char *fmt, ... );
 #endif
@@ -228,6 +244,41 @@
 #endif /* MBEDTLS_PLATFORM_SNPRINTF_ALT */
 
 /*
+ * The function pointers for vsnprintf
+ *
+ * The vsnprintf implementation should conform to C99:
+ * - it *must* always correctly zero-terminate the buffer
+ *   (except when n == 0, then it must leave the buffer untouched)
+ * - however it is acceptable to return -1 instead of the required length when
+ *   the destination buffer is too short.
+ */
+#if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_VSNPRINTF)
+/* For Older Windows (inc. MSYS2), we provide our own fixed implementation */
+int mbedtls_platform_win32_vsnprintf( char *s, size_t n, const char *fmt, va_list arg );
+#endif
+
+#if defined(MBEDTLS_PLATFORM_VSNPRINTF_ALT)
+#include <stdarg.h>
+extern int (*mbedtls_vsnprintf)( char * s, size_t n, const char * format, va_list arg );
+
+/**
+ * \brief   Set your own snprintf function pointer
+ *
+ * \param vsnprintf_func   the snprintf function implementation
+ *
+ * \return              0
+ */
+int mbedtls_platform_set_vsnprintf( int (*vsnprintf_func)( char * s, size_t n,
+                                                 const char * format, va_list arg ) );
+#else /* MBEDTLS_PLATFORM_VSNPRINTF_ALT */
+#if defined(MBEDTLS_PLATFORM_VSNPRINTF_MACRO)
+#define mbedtls_vsnprintf   MBEDTLS_PLATFORM_VSNPRINTF_MACRO
+#else
+#define mbedtls_vsnprintf   vsnprintf
+#endif /* MBEDTLS_PLATFORM_VSNPRINTF_MACRO */
+#endif /* MBEDTLS_PLATFORM_VSNPRINTF_ALT */
+
+/*
  * The function pointers for exit
  */
 #if defined(MBEDTLS_PLATFORM_EXIT_ALT)