diff --git a/CMakeLists.txt b/CMakeLists.txt
index d39151379..da65aedc4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -365,6 +365,7 @@ katie_check_function(getgrgid_r "grp.h")
 katie_check_function(nl_langinfo "langinfo.h")
 katie_check_function(getaddrinfo "netdb.h")
 katie_check_function(clock_gettime "time.h")
+katie_check_function(vsnprintf "stdio.h")
 # XSI/POSIX.1-2001
 katie_check_function(strerror_r "string.h")
 # SUSv2
diff --git a/src/core/global/qplatformdefs.h b/src/core/global/qplatformdefs.h
index a8567f079..9876c0313 100644
--- a/src/core/global/qplatformdefs.h
+++ b/src/core/global/qplatformdefs.h
@@ -154,11 +154,6 @@
 #define QT_SOCKET_CONNECT       ::connect
 #define QT_SOCKET_BIND          ::bind
 
-#if defined(_XOPEN_SOURCE) && (_XOPEN_SOURCE >= 500)
-#define QT_SNPRINTF             ::snprintf
-#define QT_VSNPRINTF            ::vsnprintf
-#endif
-
 #define QT_BUFFSIZE BUFSIZ
 
 #endif // include guard
diff --git a/src/core/tools/qvsnprintf.cpp b/src/core/tools/qvsnprintf.cpp
index 3c7c8fc80..cd92ca319 100644
--- a/src/core/tools/qvsnprintf.cpp
+++ b/src/core/tools/qvsnprintf.cpp
@@ -31,15 +31,11 @@
 **
 ****************************************************************************/
 
-#include "qplatformdefs.h"
-
 #include "qbytearray.h"
 #include "qstring.h"
 
-#include "string.h"
-#ifdef QT_VSNPRINTF
+#include <string.h>
 #include <stdio.h>
-#endif
 
 QT_BEGIN_NAMESPACE
 
@@ -67,7 +63,9 @@ QT_BEGIN_NAMESPACE
 
 int qvsnprintf(char *str, size_t n, const char *fmt, va_list ap)
 {
-#ifndef QT_VSNPRINTF
+#ifdef QT_HAVE_VSNPRINTF
+    return ::vsnprintf(str, n, fmt, ap);
+#else
     if (!str || !fmt)
         return -1;
 
@@ -83,8 +81,6 @@ int qvsnprintf(char *str, size_t n, const char *fmt, va_list ap)
     }
 
     return ba.length();
-#else
-    return QT_VSNPRINTF(str, n, fmt, ap);
 #endif
 }