diff --git a/ChangeLog b/ChangeLog
index 2789704..122cd2c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -23,6 +23,9 @@
    * Add support for alternative CSR headers, as used by Microsoft and defined
      in RFC 7468. Found by Michael Ernst. Fixes #767.
    * Correct many misspellings. Fixed by MisterDA #2371.
+   * Provide an abstraction of vsnprintf to allow alternative implementations
+     for platforms that don't provide it. Based on contributions by Joris Aerts
+     and Nathaniel Wesley Filardo.
 
 = mbed TLS 2.16.0 branch released 2018-12-21
 
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index 0f72c17..00dbeb1 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -50,6 +50,11 @@
     !defined(MBEDTLS_PLATFORM_SNPRINTF_MACRO)
 #define MBEDTLS_PLATFORM_SNPRINTF_ALT
 #endif
+
+#if !defined(MBEDTLS_PLATFORM_VSNPRINTF_ALT) && \
+    !defined(MBEDTLS_PLATFORM_VSNPRINTF_MACRO)
+#define MBEDTLS_PLATFORM_VSNPRINTF_ALT
+#endif
 #endif /* _WIN32 */
 
 #if defined(TARGET_LIKE_MBED) && \
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index c5d7bfe..f89bf96 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -226,6 +226,7 @@
 //#define MBEDTLS_PLATFORM_FPRINTF_ALT
 //#define MBEDTLS_PLATFORM_PRINTF_ALT
 //#define MBEDTLS_PLATFORM_SNPRINTF_ALT
+//#define MBEDTLS_PLATFORM_VSNPRINTF_ALT
 //#define MBEDTLS_PLATFORM_NV_SEED_ALT
 //#define MBEDTLS_PLATFORM_SETUP_TEARDOWN_ALT
 
@@ -3035,6 +3036,7 @@
 //#define MBEDTLS_PLATFORM_PRINTF_MACRO        printf /**< Default printf macro to use, can be undefined */
 /* Note: your snprintf must correctly zero-terminate the buffer! */
 //#define MBEDTLS_PLATFORM_SNPRINTF_MACRO    snprintf /**< Default snprintf macro to use, can be undefined */
+//#define MBEDTLS_PLATFORM_VSNPRINTF_MACRO    vsnprintf /**< Default vsnprintf macro to use, can be undefined */
 //#define MBEDTLS_PLATFORM_NV_SEED_READ_MACRO   mbedtls_platform_std_nv_seed_read /**< Default nv_seed_read function to use, can be undefined */
 //#define MBEDTLS_PLATFORM_NV_SEED_WRITE_MACRO  mbedtls_platform_std_nv_seed_write /**< Default nv_seed_write function to use, can be undefined */
 
diff --git a/include/mbedtls/platform.h b/include/mbedtls/platform.h
index 89fe8a7..801a948 100644
--- a/include/mbedtls/platform.h
+++ b/include/mbedtls/platform.h
@@ -58,17 +58,33 @@
  * \{
  */
 
+/* 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(__MINGW32__) || (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
@@ -204,7 +220,7 @@
  * - 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
@@ -231,6 +247,41 @@
 #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 \c vsnprintf function implementation
+ *
+ * \return  \c 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)
diff --git a/library/debug.c b/library/debug.c
index 824cd02..6e1efbf 100644
--- a/library/debug.c
+++ b/library/debug.c
@@ -35,6 +35,7 @@
 #define mbedtls_free        free
 #define mbedtls_time_t      time_t
 #define mbedtls_snprintf    snprintf
+#define mbedtls_vsnprintf   vsnprintf
 #endif
 
 #include "mbedtls/debug.h"
@@ -90,20 +91,7 @@
         return;
 
     va_start( argp, format );
-#if defined(_WIN32)
-#if defined(_TRUNCATE) && !defined(__MINGW32__)
-    ret = _vsnprintf_s( str, DEBUG_BUF_SIZE, _TRUNCATE, format, argp );
-#else
-    ret = _vsnprintf( str, DEBUG_BUF_SIZE, format, argp );
-    if( ret < 0 || (size_t) ret == DEBUG_BUF_SIZE )
-    {
-        str[DEBUG_BUF_SIZE-1] = '\0';
-        ret = -1;
-    }
-#endif
-#else
-    ret = vsnprintf( str, DEBUG_BUF_SIZE, format, argp );
-#endif
+    ret = mbedtls_vsnprintf( str, DEBUG_BUF_SIZE, format, argp );
     va_end( argp );
 
     if( ret >= 0 && ret < DEBUG_BUF_SIZE - 1 )
diff --git a/library/platform.c b/library/platform.c
index 73a6db9..5756159 100644
--- a/library/platform.c
+++ b/library/platform.c
@@ -82,28 +82,15 @@
           !( defined(MBEDTLS_PLATFORM_CALLOC_MACRO) &&
              defined(MBEDTLS_PLATFORM_FREE_MACRO) ) */
 
-#if defined(_WIN32)
+#if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_SNPRINTF)
 #include <stdarg.h>
 int mbedtls_platform_win32_snprintf( char *s, size_t n, const char *fmt, ... )
 {
     int ret;
     va_list argp;
 
-    /* Avoid calling the invalid parameter handler by checking ourselves */
-    if( s == NULL || n == 0 || fmt == NULL )
-        return( -1 );
-
     va_start( argp, fmt );
-#if defined(_TRUNCATE) && !defined(__MINGW32__)
-    ret = _vsnprintf_s( s, n, _TRUNCATE, fmt, argp );
-#else
-    ret = _vsnprintf( s, n, fmt, argp );
-    if( ret < 0 || (size_t) ret == n )
-    {
-        s[n-1] = '\0';
-        ret = -1;
-    }
-#endif
+    ret = mbedtls_vsnprintf( s, n, fmt, argp );
     va_end( argp );
 
     return( ret );
@@ -140,6 +127,62 @@
 }
 #endif /* MBEDTLS_PLATFORM_SNPRINTF_ALT */
 
+#if defined(MBEDTLS_PLATFORM_HAS_NON_CONFORMING_VSNPRINTF)
+#include <stdarg.h>
+int mbedtls_platform_win32_vsnprintf( char *s, size_t n, const char *fmt, va_list arg )
+{
+    int ret;
+
+    /* Avoid calling the invalid parameter handler by checking ourselves */
+    if( s == NULL || n == 0 || fmt == NULL )
+        return( -1 );
+
+#if defined(_TRUNCATE)
+    ret = vsnprintf_s( s, n, _TRUNCATE, fmt, arg );
+#else
+    ret = vsnprintf( s, n, fmt, arg );
+    if( ret < 0 || (size_t) ret == n )
+    {
+        s[n-1] = '\0';
+        ret = -1;
+    }
+#endif
+
+    return( ret );
+}
+#endif
+
+#if defined(MBEDTLS_PLATFORM_VSNPRINTF_ALT)
+#if !defined(MBEDTLS_PLATFORM_STD_VSNPRINTF)
+/*
+ * Make dummy function to prevent NULL pointer dereferences
+ */
+static int platform_vsnprintf_uninit( char * s, size_t n,
+                                     const char * format, va_list arg )
+{
+    ((void) s);
+    ((void) n);
+    ((void) format);
+    ((void) arg);
+    return( -1 );
+}
+
+#define MBEDTLS_PLATFORM_STD_VSNPRINTF    platform_vsnprintf_uninit
+#endif /* !MBEDTLS_PLATFORM_STD_VSNPRINTF */
+
+int (*mbedtls_vsnprintf)( char * s, size_t n,
+                          const char * format,
+                          va_list arg ) = MBEDTLS_PLATFORM_STD_VSNPRINTF;
+
+int mbedtls_platform_set_vsnprintf( int (*vsnprintf_func)( char * s, size_t n,
+                                                 const char * format,
+                                                 va_list arg ) )
+{
+    mbedtls_vsnprintf = vsnprintf_func;
+    return( 0 );
+}
+#endif /* MBEDTLS_PLATFORM_VSNPRINTF_ALT */
+
 #if defined(MBEDTLS_PLATFORM_PRINTF_ALT)
 #if !defined(MBEDTLS_PLATFORM_STD_PRINTF)
 /*
diff --git a/library/version_features.c b/library/version_features.c
index 4c36d3c..9750d20 100644
--- a/library/version_features.c
+++ b/library/version_features.c
@@ -72,6 +72,9 @@
 #if defined(MBEDTLS_PLATFORM_SNPRINTF_ALT)
     "MBEDTLS_PLATFORM_SNPRINTF_ALT",
 #endif /* MBEDTLS_PLATFORM_SNPRINTF_ALT */
+#if defined(MBEDTLS_PLATFORM_VSNPRINTF_ALT)
+    "MBEDTLS_PLATFORM_VSNPRINTF_ALT",
+#endif /* MBEDTLS_PLATFORM_VSNPRINTF_ALT */
 #if defined(MBEDTLS_PLATFORM_NV_SEED_ALT)
     "MBEDTLS_PLATFORM_NV_SEED_ALT",
 #endif /* MBEDTLS_PLATFORM_NV_SEED_ALT */